# Fertilizer TDS Nutrition and Watering



## Candace (Feb 28, 2007)

I was very surprised that in another thread, Lance mentioned he fertilized in the 500 ppm range using R.O water. Although I'm happy with my plants growth and blooming, I'd like to hear more about this. I've been keeping my fertilizer in the 150-200 range for several years and have found this is the common range most people use. I've read and been told over the years that any higher than around 200 ppm will burn leaf tips in phrags and cause problems with root growth and a myriad of other negatives in paphs and other genera. 

So, what is the ferlizer range you try to stay within? Why?


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## NYEric (Feb 28, 2007)

I think that there are great variations and innaccuracies in how people are measuring their ppm.


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## Candace (Feb 28, 2007)

Please explain. I use a TDS meter that measures in ppm.


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## NYEric (Feb 28, 2007)

The TDS [total disolved solids] will not give you the amounts of fertilizing [salts] in the water. Most TDS are giving a measure of resistance.


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## Heather (Feb 28, 2007)

I also use a TDS meter and shoot for 150ppm.


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## lothianjavert (Feb 28, 2007)

500 ppm may be high, but it is possible, depending on the ppm of the water, that much of it may not be fertilizer salts. TDS is "total dissolved solids" and includes fertilizer salts, as well as many others.

The water from our well is at about 150-200 ppm on its own. We need to do an analysis to figure out exatly what the dissovled solids are. However, our area is known for its iron concentration, so that is likely a large component. 

I have NOT noticed any leaf tips browning or any other issues, and we have been watering and fertilizing with this water for 8 months now.

At our old house, we had an RO system hooked up, as even though we had "city water", the TDS were through the roof (800 ppm BEFORE fertilizer), and no matter what we did, the phrags especially were torched. The RO was a huge improvement.


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## Candace (Feb 28, 2007)

500ppm using R.O. water just seems very high to me from all the literature and what I've been "told" over the years. Oh, Lance...


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## gonewild (Feb 28, 2007)

Eric is right the testers read the resistance in the water.
Most chemicals used to make fertilizer mixes have a resistance when dissolved in water. When we talk about the _ppm_ or _tds_ or _ec_ of the fertilizer solution we are talking about the amount of resistance in the solution. 

Here is a "simplified" explanation of how the meter works:

The meter itself works just like a meter used by electricians to measure electric current it measures electricity in volts. Our water test meters simply use a mathematical formula to change the reading into something that relates to plants. The measurement is the same. But it would not make much sense to say how many volts is your fertilizer? 1 volt = 1 ec = 500 ppm

example

My fertilizer solution is "1 volt"
My fertilizer solution is "1 ec"
My fertilizer solution is "500 ppm"

Both the volt and ec are measures of electric current. We can't easily decide how many teaspoons of fertilizer to use per gallon of water with those measurements. How do we get 1 volt of fertilizer into that gallon of water?
But if see that 1 volt is the same as 500 ppm (parts per million) we can now use a physical tool to measure the fertilizer. 

Sorry, it is not really simple and we must just accept that the meter works.
But meters need to be calibrated.


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## gonewild (Feb 28, 2007)

Candace said:


> 500ppm using R.O. water just seems very high to me from all the literature and what I've been "told" over the years. Oh, Lance...



This is what we will talk about. I want everyone to try to convince me I am wrong. Let's all learn together.

Start off with telling me (us) what literature you are going by. 
What have you been told? 

I'll tell you most articles are written by people who are quoting other people or other articles. We need to base our fertilizer knowledge on science and work done by horticulture experts, not persons passing on hearsay facts.

Rumors run wild. Someone figured out some particular orchid was sensitive to salt and now everyone is running around thinking you'll burn your orchids up if you fertilize them. A classic example of "Chicken Little".


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## gonewild (Feb 28, 2007)

Heather said:


> I also use a TDS meter and shoot for 150ppm.



Why 150 ppm?


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## gonewild (Feb 28, 2007)

Candace said:


> I've read and been told over the years that any higher than around 200 ppm will burn leaf tips in phrags and cause problems with root growth and a myriad of other negatives in paphs and other genera.



Do we have some research that proves or even states that 200 ppm will burn leaf tips on phrags? Or is this just a number someone picked because they new it was safe?

Do we know if it is a high level of total salts that burns the leaf tips or is it one salt in particular that the plants are sensitive to?


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## gonewild (Feb 28, 2007)

lothianjavert said:


> 500 ppm may be high, but it is possible, depending on the ppm of the water, that much of it may not be fertilizer salts. TDS is "total dissolved solids" and includes fertilizer salts, as well as many others.



Correct, it depends on the water supply. But when I refer to 500 ppm fertilizer solution that includes any salts from the water source. in my case I'm getting 18 ppm from my RO water source.



> The water from our well is at about 150-200 ppm on its own. We need to do an analysis to figure out exatly what the dissovled solids are. However, our area is known for its iron concentration, so that is likely a large component.



Yes and you need to know what form the iron is in. Excess minerals can cause problems with other minerals. Nutrient requirements of plants are not simple and an excess of one mineral may mean a deficiency of another and vice versa, a deficiency on one mineral may make excess of another toxic.
It is all about _balance_.



> I have NOT noticed any leaf tips browning or any other issues, and we have been watering and fertilizing with this water for 8 months now.



Do you know what the ppm of your fertilizer solution is? (fertilizer in well water)



> At our old house, we had an RO system hooked up, as even though we had "city water", the TDS were through the roof (800 ppm BEFORE fertilizer), and no matter what we did, the phrags especially were torched. The RO was a huge improvement.



It would be interesting to know if it was the 800 ppm total that "torched" the phrags or was it an excess of certain minerals?


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## gonewild (Feb 28, 2007)

Calibrate your ppm tester:

Mix 1 gram of table salt in 500 ml of pure (distilled or RO) water.
Dissolve thouroghly. 
test with your meter.
Your meter should read 2000ppm or a little more if you used RO water.

Now carefully measure out 250 ml of the salt water.
Mix it with 250 ml of pure water to have a 500 ml total.
Now your meter should measure this as 1000 ppm.

Now carefully measure out 250 ml of the last salt water.
Mix it with 250 ml of pure water to have a 500 ml total.
Now your meter should measure this as 500 ppm.

Now carefully measure out 250 ml of the last salt water.
Mix it with 250 ml of pure water to have a 500 ml total.
Now your meter should measure this as 250 ppm.

Now carefully measure out 250 ml of the last salt water.
Mix it with 250 ml of pure water to have a 500 ml total.
Now your meter should measure this as 125 ppm.

Keep doing this as long as it remains fun. But you cant go past 0 ppm oke: 

If your meter is accurate it should read the ppm for the concentrations above. If it is close but not exact don't worry.


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## gonewild (Feb 28, 2007)

I think the biggest misconception here is the measurement between total ppm and ppm of the nitrogen.

We'll use Rays recommendation of a constant feed of 125 ppm. That is meant to supply 125 ppm of actual nitrogen. To do this you end up with a much higher reading of the irrigation water because of the other minerals (salts) dissolved in the solution. You can't have a total ppm level of 150 and have 125 ppm of it being nitrogen. That is unless you are using a fertilizer that contains basically only Nitrogen.


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## lothianjavert (Feb 28, 2007)

With the water at the old house, the water source was from the Susquehanna River at the head of the Chesapeake Bay-- so you had not only some salinity from the bay itself, depending on tide and water levels, you also had an incredible amount of agricultural runoff. The local treatment plants do not operate on RO, so all salts generally stayed. Water was clarified (particulates were filtered out and allowed to "settle", and chlorine was added, as well as a solution to raise the pH and buffer the water. 

Hence, even w/o adding fertilizer, you already have a concentration of the salts, plus any resident salts from the bay. You know it's bad when at times the local newspaper advises those that need to watch their salt intake not to drink the water. 

I do need to know what the iron content of the current water is, and in what form-- I understand that it's all about balance. Same thing w/ human nutrition. i.e. Vit. D is needed for calcium absorption, etc.

It'll either be sending away, or I'll check and see if my uncle can do it for me at his city's water plant, as they have a full lab there.


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## gonewild (Feb 28, 2007)

lothianjavert said:


> With the water at the old house, the water source was from the Susquehanna River at the head of the Chesapeake Bay-- so you had not only some salinity from the bay itself, depending on tide and water levels, you also had an incredible amount of agricultural runoff. The local treatment plants do not operate on RO, so all salts generally stayed. Water was clarified (particulates were filtered out and allowed to "settle", and chlorine was added, as well as a solution to raise the pH and buffer the water.
> 
> Hence, even w/o adding fertilizer, you already have a concentration of the salts, plus any resident salts from the bay. You know it's bad when at times the local newspaper advises those that need to watch their salt intake not to drink the water.
> 
> ...



Then the problem you had at the old place with your phrags being "torched" was probably due to a high sodium content level rather than the total tds in general.

So what I suggest is that maybe 800 ppm should not be assumed to be toxic just because it is a big number compared to 150 ppm.


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## Candace (Feb 28, 2007)

O.K. so how do we figure out what ppm of nitrogen we are using? I may indeed be underfertilizing as I've just added enough of whatever fertilizer I'm using to around 150-175 ppm. with my meter.


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## gonewild (Feb 28, 2007)

Candace said:


> O.K. so how do we figure out what ppm of nitrogen we are using? I may indeed be underfertilizing as I've just added enough of whatever fertilizer I'm using to around 150-175 ppm. with my meter.



Read the label on the fertilizer. If it says it has 20% nitrogen then approximately 20% of the "salts" you are adding are pure nitrogen.


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## gonewild (Feb 28, 2007)

gonewild said:


> Read the label on the fertilizer. If it says it has 20% nitrogen then approximately 20% of the "salts" you are adding are pure nitrogen.




Let me explain by example...

Fertilizer labels are as important to plants as food labels are to people.

If you start with RO water at 0 ppm and add enough fertilizer to make it read 150 ppm your total ppm is 150.

Now look at the contents of your fertilizer. If it is 20% nitrogen then 20% of your 150 ppm's is elemental nitrogen. When you do the math:

150 ppm x 20% = 30 ppm of nitrogen.

If you want to have 150 ppm of nitrogen in your irrigation water you need to add 5 times more fertilizer.

30 ppm nitrogen x 5 = 150 ppm of nitrogen.

This will make your fertilizer solution about 750 ppm.

*This is an example only and not a recommendation*. There are other factors involved depending on what else your fertilizer contains.


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## Candace (Feb 28, 2007)

Thanks for the explanation, Lance. By the looks of it, I've been underutilizing my fertilizers. If I like what I'm getting now, I'm hopeful I'll see even more growth and blooms if I up it a little. :drool: I'm going to increase it slowly and see what, if any results I see. And I'm going to use my MSU more regularly so I won't have to worry about any ph mishaps.


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## gonewild (Feb 28, 2007)

Candace said:


> Thanks for the explanation, Lance. By the looks of it, I've been underutilizing my fertilizers. If I like what I'm getting now, I'm hopeful I'll see even more growth and blooms if I up it a little. :drool: I'm going to increase it slowly and see what, if any results I see. And I'm going to use my MSU more regularly so I won't have to worry about any ph mishaps.



Using the MSU formula always will assure you are keeping the correct nutrient balance which is really very important. It really is a well formulated recipe. FYI... I use about 2/3 tbs per gallon.


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## Heather (Feb 28, 2007)

Interesting...I need to measure my water again sometime soon and analyze all of this again, but it makes no difference now, might as well wait until the plants are moved to their new home.


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## gonewild (Feb 28, 2007)

Heather said:


> Interesting...I need to measure my water again sometime soon and analyze all of this again, but it makes no difference now, might as well wait until the plants are moved to their new home.



You should measure it now and figure out and understand what you have been doing. That way when you start over at the new place you will know what you actually were doing in the past. You need to know and remember what you have done so you can better decide what to do.
Why waste all that knowledge?


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## NYEric (Mar 1, 2007)

I hate having to calibrate the meter.


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## NYEric (Mar 1, 2007)

gonewild said:


> You should measure it now and figure out and understand what you have been doing. That way when you start over at the new place you will know what you actually were doing in the past. You need to know and remember what you have done so you can better decide what to do.
> Why waste all that knowledge?


Correct. I am keeping track of one tray that I fertilize the old way and the new MSU weekly.


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## NYEric (Mar 1, 2007)

gonewild said:


> FYI... I use about 2/3 tbs per gallon.


Is that the recommended rate of application?oke:


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## IdahoOrchid (Mar 1, 2007)

gonewild said:


> I use about 2/3 tbs per gallon.


And you ALWAYS water with the fertilizer? (what my mother in law calls "orchid water") Never a clear water flush on your media?


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## Heather (Mar 1, 2007)

Don't forget, Lance waters a bit differently from the rest of most of us. Misting several times a day, right? Would you call that foliar feeding, Lance? Or am I mixing my metaphors here?


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## Candace (Mar 1, 2007)

Watering at least twice a day must be a real PITA, if he does it by hand.


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## dave b (Mar 1, 2007)

Definitely follow the specific dosage recommended for each fertilizer, as they are not all the same. For example...Scotts website posts some data concerning the popular Peter's 20-20-20. 1 level teaspoon per gallon results in a concentration of approx 240ppm N (nitrogen). A good amount. Whereas, 1 tablespoon per gallon = 720 ppm N (way too high).

Also remember that different ions (N, P, K, Cu, Fe, Mg..etc.) in solution have different conductivities from each other. They dont all conduct the same. The 'metal' salts have higher conductivities, and would greatly affect the total tds / ppm reading of a fertilizer solution.


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## IdahoOrchid (Mar 1, 2007)

I have read that one should avoid the use of ammonium nitrate (no3) as a source of nitrogen. The person discussed as the source of the information is Xavier Garreu de Loubresse. I don't know who he is. Apparently there are detrimental affects that are possible.

What are your thoughts on this?


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## dave b (Mar 1, 2007)

From an environmental standpoint, nitrates (NO3) can be easilly washed away from yards, golf courses, and farm fields. It ends up in our rivers, and ground water supplies which is not good. It can contribute to unnattural algae blooms, and even build to toxic levels killing fish and other organisms. Most fertilizers provide N in 3 ways. Ammonium (NH4)...its safer, because it cant wash away easier in soils, it is also converted to NO3 (second method) by bacteria. And third, urea. Some research suggests that urea bound N is not available unless in soils where beneficial bacteria / fungi can break it down to usable sources. many orchid fertilizers will state that they dont use urea based N because of this. Our orchid medias dont harbor the necessary microorganisms.

Whether i answered your question, is another story.


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## gonewild (Mar 2, 2007)

NYEric said:


> Is that the recommended rate of application?oke:



Actually I think it is a little less than the "recommended" rate. I started with a lower rate and worked up to this with the besseae hybrids. I think it is a safe amount and I also think it is enough. If you have light and temperature that promotes fast growth you could easily use a little more. If you have darker cooler conditions you might want to reduce it a little.

There really is not a known "best" rate for phrags. The MSU formula was found to be ideal for orchids in general at a rate of about 125 ppm of nitrogen as a constant feed.

It works well for us.


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## gonewild (Mar 2, 2007)

NYEric said:


> I hate having to calibrate the meter.



You don't really need to calibrate it, just check it to see if it is fairly accurate.


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## gonewild (Mar 2, 2007)

IdahoOrchid said:


> And you ALWAYS water with the fertilizer? (what my mother in law calls "orchid water") Never a clear water flush on your media?



Yes. But I'm not suggesting you shouldn't occasionally water with clear water. If you are applying enough fertilizer water to keep excess salts from accumulating there is no need to use clear water. The idea is to always have the nutrients available for the plants. If you water with clear water then soon after water them with fertilizer water (same day, next day, no big deal).

Flushing with fertilizer water will flush away the salts just as well as clear water so why confuse the issue.


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## gonewild (Mar 2, 2007)

Heather said:


> Don't forget, Lance waters a bit differently from the rest of most of us. Misting several times a day, right? Would you call that foliar feeding, Lance? Or am I mixing my metaphors here?



Yes, I guess I am a bit different! We apply fertilizer water fairly heavy in the morning, then again lightly after lunch. The fertilizer water is applied with a overhead spray. Depending on the humidity and temperature we also mist with a very fine mist nozzle several times per day, but this mist is clear RO water.

And yes, this is foliar feeding as well as root irrigation. Plants can intake a tremendous amount of nutrients through their foliage. It really gives a plant a source of nutrients easy to intake. It is especially good for small seedlings that don't have a lot of active roots yet (out of flask). It is also good for older plants that may be having root problems. AND for those stubborn plants that don't want to grow very many roots.


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## gonewild (Mar 2, 2007)

Candace said:


> Watering at least twice a day must be a real PITA, if he does it by hand.



Ah Ha! It could be a PITA but not if you enjoy watching the plants grow!

Actually I am very fortunate, my wife loves to water the seedlings and does most of it. OK all of it. :clap: 

If the watering was automated they would get watered even more times per day!


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## gonewild (Mar 2, 2007)

dave b said:


> Also remember that different ions (N, P, K, Cu, Fe, Mg..etc.) in solution have different conductivities from each other. They dont all conduct the same. The 'metal' salts have higher conductivities, and would greatly affect the total tds / ppm reading of a fertilizer solution.



That is correct and this factor has been taken into consideration with the ppm amounts I suggest.


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## gonewild (Mar 2, 2007)

IdahoOrchid said:


> I have read that one should avoid the use of ammonium nitrate (no3) as a source of nitrogen. The person discussed as the source of the information is Xavier Garreu de Loubresse. I don't know who he is. Apparently there are detrimental affects that are possible.
> 
> What are your thoughts on this?



I've never had problems with Ammonium nitrate, when applied correctly, but I prefer Calcium nitrate and Potassium nitrate as sources for nitrogen on delicate potted plants.

Sometimes you might want to limit the potassium or calcium in your nutrient solution and Ammonium nitrate is really the other good source.

Do you know what were the specific problems he had?


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## gonewild (Mar 2, 2007)

dave b said:


> From an environmental standpoint, nitrates (NO3) can be easilly washed away from yards, golf courses, and farm fields. It ends up in our rivers, and ground water supplies which is not good. It can contribute to unnattural algae blooms, and even build to toxic levels killing fish and other organisms. Most fertilizers provide N in 3 ways. Ammonium (NH4)...its safer, because it cant wash away easier in soils, it is also converted to NO3 (second method) by bacteria. And third, urea. Some research suggests that urea bound N is not available unless in soils where beneficial bacteria / fungi can break it down to usable sources. many orchid fertilizers will state that they dont use urea based N because of this. Our orchid medias dont harbor the necessary microorganisms.
> 
> Whether i answered your question, is another story.



I would avoid fertilizers that contain Urea for use on orchids. Urea is the cheapest source of nitrogen. The only reason to use it in a fertilizer blend is because it is cheap. When you see it on the content label that should be a signal that the manufacturer may not use the best ingredients. Choose another brand.


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## NYEric (Mar 2, 2007)

I got a Urea free formula but I mix it 1:1 w/ a formula that has urea. [I stopped using this for my Phrags though, and went to a weak MSU solution.] I think I have to up my fertilizer routine a little because I do have so much light and energy in the growing area. I guess my method differs from Lance's because my plants are always in the water solution.


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## lothianjavert (Mar 2, 2007)

I've been using the MSU since July, and really like it.


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## IdahoOrchid (Mar 2, 2007)

gonewild said:


> I've never had problems with Ammonium nitrate, when applied correctly, but I prefer Calcium nitrate and Potassium nitrate as sources for nitrogen on delicate potted plants.
> 
> Sometimes you might want to limit the potassium or calcium in your nutrient solution and Ammonium nitrate is really the other good source.
> 
> Do you know what were the specific problems he had?



I misspoke when I mentioned ammonium. It is just NO3 (nitrate) that was mentioned. Nothing specific other than it typically caused death in paphs and the gentleman mentioned as the main source of the info.


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## Ray (Mar 3, 2007)

Lance's recommendation about calibrating a TDS meter is a good one, although I'm not sure I'd use table salt to do so. (Then again, I don't know how much it really matters, so he could be close enough.)

TDS meters just measure electrical conductivity of the solution and add an arbitrary conversion factor. EC is determined by the ionic mobility of the dissolved species. If you add table salt to pure water, the only things contributing to the EC are Cl- and Na+, which are both small in diameter so move easily in the solution. An ion of the same size but twice the charge moves twice as fast, while one with twice the size and the same charge moves half as quickly. Because of those ionic mobility differences, that conversion factor needs to be different depending on the exact chemical makeup of the solution.

Using the EC and concentration data from Blackmore, and a conductivity standard, I calibrated my two meters. At 150 ppm N of the MSU RO formulation, the calculated TDS contribution from the fertilizer should be about 425 ppm. My two meters told me about 600 and 750!

That is not a problem, however, as I now know that if I measure the TDS at those levels, I am _really_ getting the 150 ppm N. If, on the other hand, I use them and see 425 ppm and trust it at face value, I'm actually underfeeding.


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## Rick (Mar 3, 2007)

dave b said:


> From an environmental standpoint, nitrates (NO3) can be easilly washed away from yards, golf courses, and farm fields. It ends up in our rivers, and ground water supplies which is not good. It can contribute to unnattural algae blooms, and even build to toxic levels killing fish and other organisms. Most fertilizers provide N in 3 ways. Ammonium (NH4)...its safer, because it cant wash away easier in soils, it is also converted to NO3 (second method) by bacteria. And third, urea. Some research suggests that urea bound N is not available unless in soils where beneficial bacteria / fungi can break it down to usable sources. many orchid fertilizers will state that they dont use urea based N because of this. Our orchid medias dont harbor the necessary microorganisms.
> 
> Whether i answered your question, is another story.



I work with these materials allot as an aquatic toxicologist. Ammonia is a very toxic compound compared to nitrate. Its toxicity is pH dependent. The higher the pH the more toxic, with the highest toxicity in the pH range of 8-9 s.u. (generally out of soil pH ranges). The toxicity of nitrate is orders of magnitude less than for amonia and its first bio-oxidation product nitrite. Orchids will utilize ammonia and nitrate fairly well as nutrients, but the levels to achieve toxicity (as opposed to growth) will be less for amonia than nitrate. Subsequently it may be argued that the best source of nitrogen for orchids would be calcium nitrate. Your are correct that urea cannot be utilized by plants without microbial intervention. Urea fertilizers are popular with agri-crop species with lots of soil bacteria present.


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## gonewild (Mar 3, 2007)

Rick said:


> I work with these materials allot as an aquatic toxicologist. Ammonia is a very toxic compound compared to nitrate. Its toxicity is pH dependent. The higher the pH the more toxic, with the highest toxicity in the pH range of 8-9 s.u. (generally out of soil pH ranges). The toxicity of nitrate is orders of magnitude less than for amonia and its first bio-oxidation product nitrite. Orchids will utilize ammonia and nitrate fairly well as nutrients, but the levels to achieve toxicity (as opposed to growth) will be less for amonia than nitrate. Subsequently it may be argued that the best source of nitrogen for orchids would be calcium nitrate. Your are correct that urea cannot be utilized by plants without microbial intervention. Urea fertilizers are popular with agri-crop species with lots of soil bacteria present.



Urea releases ammonia as a gas when it is in contact with the atmosphere so based on what you say that is even more reason to avoid it.


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## gonewild (Mar 3, 2007)

Ray said:


> Lance's recommendation about calibrating a TDS meter is a good one, although I'm not sure I'd use table salt to do so. (Then again, I don't know how much it really matters, so he could be close enough.)
> 
> TDS meters just measure electrical conductivity of the solution and add an arbitrary conversion factor. EC is determined by the ionic mobility of the dissolved species. If you add table salt to pure water, the only things contributing to the EC are Cl- and Na+, which are both small in diameter so move easily in the solution. An ion of the same size but twice the charge moves twice as fast, while one with twice the size and the same charge moves half as quickly. Because of those ionic mobility differences, that conversion factor needs to be different depending on the exact chemical makeup of the solution.



Table salt is good to use to calibrate a meter because it is something everyone has. When mixed at exact ratios it provides an accurate known ppm to calibrate by.

It is not practical to have a seperate meter adjusted for each fertilizer element. It is also not reasonable to expect hobbyist growers to spend $300 on an accurate ec meter. So what we need to do is talk in terms of readings from ppm testers that everyone can afford ($20-$30). When calibrated to a table salt solution the accuracy is good enough to use for growing plants.

The cheap ppm tester I bought came calibrated very accurately and I felt no need to adjust it or compensate for the error.



> Using the EC and concentration data from Blackmore, and a conductivity standard, I calibrated my two meters. At 150 ppm N of the MSU RO formulation, the calculated TDS contribution from the fertilizer should be about 425 ppm. My two meters told me about 600 and 750!



How did you make the fertilizer solution you tested? Measuring by weight or volume?

Above you say with 150 ppm N the total is 425 ppm.
On your web page you say 125 ppm N is 475 ppm total.

You written numbers don't support each other, can you define which is correct?

This is a quote from your website:
"As I typically shoot for 100-125 ppm N in my fertilizer solution, I simply use my TDS meters as a check, knowing that the Hanna TDS1 should show between 380 and 475 ppm TDS,"



> That is not a problem, however, as I now know that if I measure the TDS at those levels, I am _really_ getting the 150 ppm N. If, on the other hand, I use them and see 425 ppm and trust it at face value, I'm actually underfeeding.



I think the best thing for most folks to do is to trust the label on the fertilizer to start with. Then use the meter to make sure the concentrations in their pots are remaining at a safe level.

If you want to maintain 150 ppm of nitrogen and use a meter to keep track of the concentration here is a plan to follow....

(choose your desired nitrogen level, 150 ppm is used as an example only)

1. Make a table salt solution to calibrate your test meter. Save this solution to check your test meter in the future. Make a note as to what reading the meter gives for future reference

2.The label on the MSU (13-3-15) says to use 1 tsp per gallon to get 150 ppm. Use 1 tsp per gallon and trust it is correct.

3. Measure the total ppm with your test meter and remember this as the total ppm.

4. Periodically check the water in your pot reservoir or the small amout of water that drains from the pot with the same test meter to see how it compares to the original total. If your ppm levels remain at or near the original level you are basically fertilizing correctly. If your levels are contstantly lower either your plants are consuming the nutrients or you are adding fresh water that dilutes the solution in the pot. If the concentration is lower you can safely increase the amount of fertilizer you are using. If the concentration is higher you should flush the media more often. 

5. Occasionally test your meter by taking a reading of your saved table salt solution you made in step #1. If the meter no longer reads the same as when you first tested the solution you need to calibrate your meter's readout or get a new meter. If it is only of by a small amount don't worry about it.


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## dave b (Mar 3, 2007)

Rick said:


> I work with these materials allot as an aquatic toxicologist. Ammonia is a very toxic compound compared to nitrate. Its toxicity is pH dependent. The higher the pH the more toxic, with the highest toxicity in the pH range of 8-9 s.u. (generally out of soil pH ranges). The toxicity of nitrate is orders of magnitude less than for amonia and its first bio-oxidation product nitrite. Orchids will utilize ammonia and nitrate fairly well as nutrients, but the levels to achieve toxicity (as opposed to growth) will be less for amonia than nitrate. Subsequently it may be argued that the best source of nitrogen for orchids would be calcium nitrate. Your are correct that urea cannot be utilized by plants without microbial intervention. Urea fertilizers are popular with agri-crop species with lots of soil bacteria present.



Great info, good to have an expert on hand. You've got me wondering now. Is the ammonia (NH3) in the nitrogen cycle you mentioned (bio-oxidation) interchangeable with the ammonium (NH4) of fertilizers? I know enough to only be dangerous. Ammonia is broken down by bacteria which produce the nitrite, then by another to nitrate. Is ammonium broken down in the same manner? Do they contribute N in the same way to plants? Forgive me if im starting to get too far out into left field.


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## Rick (Mar 3, 2007)

You've picked up on the bio-oxidation pathway that aquarists and waste-water treatment engineers have been utilizing for years for amonia management. The conversion from amonia to amonium is a pH dependent process that also is important since the higher the pH the higher the percentage of unionized amonium (the most toxic form) ion is available. Therefore regardless of what the bottle says is the form of ammonia (NH3, or NH4+) it will change from one form to another in a ratio that is pH and temperature dependent. Another way to get rid of amonia from water is to raise the pH to 10 (to convert all the amonia to the volitile unionized form) and airstrip it off.

Nitrifying bacteria need an alkalinity source (i.e moderate pH environment) to dump the hydrogens from the ammonia as they oxidize it to nitrite and then nitrate, but if you raise the pH up to high the percentage of toxic amonia goes up to much and kills them too. if the pH drops to low they can't nitrify, and the amonia goes untouched. Much of this is irrelavent to orchids and fish that don't nitrify, but experience ammonia toxicity primarily on the basis of the percent of free ammonia as the pH goes up.


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## Rick (Mar 3, 2007)

The industry (or ASTM) standard for calibrating conductivity meters is with potassium chloride at 25C. But sodium chloride is a pretty stable standard too, especially in the temperature range we grow our plants in.

There are 2 different algorithems that are used in TDS meters to convert from conductivity to TDS. Most use a TDS based on sugar (I think sucrose). Others use NaCl. I don't know of any "TDS" meters that use both or have an option to use one or the other, but as pointed out in several prevous posts, the algorithm is an approximation to aqueous mixtures of salts where the conductance vs concentration of various salt species varies with the individual salt species. The ASTM method for determining TDS is to evaporate all the water from a measured quantity of solution and weigh the resulting residue of salts left. Meters are much faster, and can obviously used on the spot compared to the ASTM method. So in most cases a TDS meter calibrated to NaCl is close enough for orchid use.


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## Ray (Mar 4, 2007)

Lance,

As I said, you might be right about the calibration with salt. I guess my chemistry and engineering background forces me to question it - I did say that I don't know it's wrong!

TDS is a mass-per-mass measurement. I did some calculating from fertilizer labels. One gram of fertilizer contains the following grams of nutrients:

Greencare "MSU" Pure Water - 0.374427
Greencare "MSU" Well Water - 0.406099
Dyna-Gro "Grow" - 0.181006
Dyna-Gro "Bloom" - 0.162799

There are several problems with converting those values to TDS. For one, many of the listed nutrients are expressed as elements, so without "backing" your way into the formula of ingredients, you really don't know how much is contributed by the rest of the minerals that contributed the element. With Dyna-Gro we know that much of the formula is water, but in the powders, we're not taking into account 60%!

Then there's the question of how many grams in a teaspoon, and how inaccurately we measure teaspoons. 425 ppm or 475 ppm is irrelevant considering.

All that said, I believe it's best to control your fertilizer concentration by EC, not TDS. Doing some digging among professional growers and several fertilizer producers, I have learned that apparently we orchid growers are somewhat unique in the use of TDS rather than EC. I wonder why?


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## IdahoOrchid (Mar 4, 2007)

Ray said:


> All that said, I believe it's best to control your fertilizer concentration by EC, not TDS. Doing some digging among professional growers and several fertilizer producers, I have learned that apparently we orchid growers are somewhat unique in the use of TDS rather than EC. I wonder why?


The cost of taking the measurement, maybe?


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## Heather (Mar 4, 2007)

I don't think people understand EC, I know I don't, so I go by TDS which I actually understand. 

People have explained it to me ad nauseum, but I just don't get it. I'm too visual.


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## gonewild (Mar 4, 2007)

Ray said:


> As I said, you might be right about the calibration with salt. I guess my chemistry and engineering background forces me to question it - I did say that I don't know it's wrong!



Well there really is no right or wrong with which salt you choose to make a calabration solution as long as it is mixed at an exact amount. I suggest table salt because everyone has it in the kitchen. To use a lab solution people have to purchase it. I just think for hobby growers it is best to keep it as simple and easy as possible.



> TDS is a mass-per-mass measurement. I did some calculating from fertilizer labels. One gram of fertilizer contains the following grams of nutrients:
> 
> Greencare "MSU" Pure Water - 0.374427
> Greencare "MSU" Well Water - 0.406099
> ...



I would have thought the Pure Water formula would have had more nutrients per gram than the Well Water formula. So with the Dyna grow you get quite a bit less value for your money$



> There are several problems with converting those values to TDS. For one, many of the listed nutrients are expressed as elements, so without "backing" your way into the formula of ingredients, you really don't know how much is contributed by the rest of the minerals that contributed the element. With Dyna-Gro we know that much of the formula is water, but in the powders, we're not taking into account 60%!



This is exactly why I suggest people trust the label recommendations for the amount to mix per gallon. Perhaps the MSU formula has more reason to trust it since they did such an extensive trial to develop the recipe. Once you have made the recommended mix you can establish the PPM(TDS) total. It does not really matter whether the meter total says 500 ppm or 600 ppm as long as the nutrient balance is correct and the total salts are not dangerously high for the plants you are using it on.



> Then there's the question of how many grams in a teaspoon, and how inaccurately we measure teaspoons. 425 ppm or 475 ppm is irrelevant considering.



When I started using the MSU formula I measured it in grams to establish my benchmark concentration. The accuracy of teaspoon measurement can be off by several hundred ppm, this is another reason to test the ppm often. But 500 ppm is well under the danger level for most plants.



> All that said, I believe it's best to control your fertilizer concentration by EC, not TDS. Doing some digging among professional growers and several fertilizer producers, I have learned that apparently we orchid growers are somewhat unique in the use of TDS rather than EC. I wonder why?



The reason we orchid growers use tds or ppm meters is because they cost $30 instead of $300. We would rather buy plants. Professional growers and consultants need nice toys to impress themselves and their clients. Now nobody take offense.  

EC and TDS are really the same thing. Just a different name for the same amount of electroconductivity. 1 EC = 500 ppm of NaCl.
PPM or TDS just converts the reading into an easy to relate to measurement.
In the past I have always used EC meters. Not until I returned from Peru did I even know you could buy an inexpensive meter that read in PPM. I bought one to try it out and found it is accurate enough to use for growing orchids. 

It is like the speedometer on a car being in mph or kph or which measurement do you use in the kitchen 1 cup or 8 oz?


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## gonewild (Mar 4, 2007)

IdahoOrchid said:


> The cost of taking the measurement, maybe?



Yes.


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## IdahoOrchid (Mar 4, 2007)

gonewild said:


> 1 EC = 500 ppm of NaCl



Is this related to conductivity in electronics: ie E = I * R (Ohms Law) Voltage = Current * Resistance

I assume that EC would be related to the current portion ( the I ) in that formula. If so, how does it relate?


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## gonewild (Mar 4, 2007)

IdahoOrchid said:


> Is this related to conductivity in electronics: ie E = I * R (Ohms Law) Voltage = Current * Resistance
> 
> I assume that EC would be related to the current portion ( the I ) in that formula. If so, how does it relate?



Not only is it related, that is exactly what it is. The resistance between two probes at a fixed distance is measured in microsiemens which can be converted into OHMS or volts or EC or PPM or any other way you want to express the result.

Here are a couple of web pages that explain the basics of Electro conductivity measurement:

http://www.octiva.net/projects/ppm/

http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.php


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## gonewild (Mar 4, 2007)

Heather said:


> I don't think people understand EC, I know I don't, so I go by TDS which I actually understand.
> 
> People have explained it to me ad nauseum, but I just don't get it. I'm too visual.



It is easier to relate to TDS (PPM) than EC because it is volume related as opposed to electrical current. 

I don't think it is worth the time trying to understand the difference.

Use whatever meter you have or can afford to check the levels of your fertilizer solution and the solution in your pots. It does not matter what read out formula the tester shows. The point is to be able to keep your nutrient levels correct by detecting and comparing changes that might occur.

Just remember when you take advice from someone about fertilizer solutions to make sure that your meter speaks the same language as theirs. 
For example, If I tell you to use "10 on the meter" make sure if I mean 10 PPM or 10 EC. There is a huge difference. 
If I were to tell you to mix your MSU fertilizer to a total strength of 1.0 EC how would you ever know how many teaspoons to start with? But if I told you to mix it to a total strength of 500 ppm you could probably figure out from the fertilizer label to start with about 1 teaspoon.


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## Heather (Mar 4, 2007)

gonewild said:


> It is easier to relate to TDS (PPM) than EC because it is volume related as opposed to electrical current.
> 
> I don't think it is worth the time trying to understand the difference.



Thanks Lance, that's sort of how I look at it too. I have a very hard time understanding things I cannot visualize (definitely a visual learner!) so things like this (and MATH!) have always been really difficult for me. You could explain it to me until you were blue in the face but I still wouldn't get it. I wish that teachers had understood about multiple intelligences back when I was in elem/middle/high school.


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## gonewild (Mar 4, 2007)

Heather said:


> Thanks Lance, that's sort of how I look at it too. I have a very hard time understanding things I cannot visualize (definitely a visual learner!) so things like this (and MATH!) have always been really difficult for me. You could explain it to me until you were blue in the face but I still wouldn't get it. I wish that teachers had understood about multiple intelligences back when I was in elem/middle/high school.



Great, so just use your meter to help give you clues why your plants look the way they do. The very best growers grow visually and only use meters to prevent future problems before they become visual.. 

Meters are for comparing information either from your own memory or to help you make decisions based on other peoples experience. 

A doctor does not need a thermometer to determine if a patient has a temperature. But he may want to know if the fever is a 101For 104F.(does not matter if he reads it in Fahrenheit or Celsius as long as he knows which it is does it?)


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## IdahoOrchid (Mar 4, 2007)

I found this page that has some testers and information:

http://www.watercenter.com/category... Meters, Testers and Probes&Cart=114106376557

I am not sure how we might use this but it does have some good descriptions and instruction:

http://wwwchem.csustan.edu/CHEM2000/EXP6/exp6a.htm

Here is where hand held meter *could* help get more accurate measurements than the LED indicator in the article. Measure the voltage across the resistor and you should be able to get a finer indication of the solution. Just remember that the strength of the battery can/will have an effect on the result. I imagine the same is true for most other meters unless they are designed to us a smaller voltage than the suppy provides.

Even better, a "cheap" tester that will do both EC *and* PPM testing:

http://www.labsafety.com/store/item/100723/

Heck, do a seach (I use metacrawler.com) on conductivity tester and you will find ALL and MORE than you ever wanted to know on this.


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## gonewild (Mar 4, 2007)

IdahoOrchid said:


> I found this page that has some testers and information:
> 
> http://www.watercenter.com/category... Meters, Testers and Probes&Cart=114106376557
> 
> ...



This is the one I am using. Cheapest I could find. I works fine. I think all of the cheaper models probably are made the same, just put into a different case. Unless you buy a really good meter you may as well spend as little as possible.


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## NYEric (Mar 5, 2007)

Lance, on the meter what units does it say it measures in, microns/CM3?


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## Candace (Mar 5, 2007)

I had to replace my cheapo Hanna meter that I dropped and broke. I got one on ebay for 9.99 plus shipping. It came yesterday and I'm not going to go through all the calibration stuff as what it states is good enough for my purposes. My R.O. in the greenhouse is 3 and my indoor R.O. for my drinking water came in at 8. Both were around where my last meter read. I've got to keep an eye on my indoor filters and replace. It's been at least 6 months since I've replaced my indoor filter.


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## gonewild (Mar 5, 2007)

NYEric said:


> Lance, on the meter what units does it say it measures in, microns/CM3?



The one I have says TDS and PPM.

microns/CM3 probably is _microSiemens / cubic centimeter_ which would be in the EC scale.


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## gonewild (Mar 5, 2007)

Candace said:


> I had to replace my cheapo Hanna meter that I dropped and broke. I got one on ebay for 9.99 plus shipping. It came yesterday and I'm not going to go through all the calibration stuff as what it states is good enough for my purposes. My R.O. in the greenhouse is 3 and my indoor R.O. for my drinking water came in at 8. Both were around where my last meter read. I've got to keep an eye on my indoor filters and replace. It's been at least 6 months since I've replaced my indoor filter.



Lucky you did not drop an expensive EC meter!


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## gonewild (Mar 5, 2007)

For those of you who still don't understand meters, Here is a link to a page that explains very clearly the difference between EC and TDS / PPM. Go figure the marijuana growers could explain it simply. :clap:


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