# TDS numbers



## rcb (Jun 14, 2013)

I've been collecting some TDS numbers over the last month. What do you all think?

Tap water - 50 - 70ppm TDS.

Fertilizer water - avg about 850ppm TDS. (25/75 MSU/K-lite)

Rain water (collected as free fall not run off) - 9 - 17ppm TDS.

And then one day, after about 2 inches of rain had fallen, I squeezed out spag that was in a pot, 132ppm TDS. (This was suprising as I've always been told that spag "holds" fertilizer salts.)

And at the same time, I set one of my Catts (potted in LECA) in a cup, allowed just enough more rain to fall to collect, and TDS was 98ppm TDS. I should have done this as it was first raining, but couldn't.

Do these make sense? - especially the water collected after rainfall from the pots - I am taking this as the rain does significantly flush the pots.


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## gonewild (Jun 14, 2013)

rcb said:


> Fertilizer water - avg about 850ppm TDS. (25/75 MSU/K-lite)



Pretty strong.


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## Trithor (Jun 14, 2013)

gonewild said:


> Pretty strong.



What would you say it should be ?


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## Rick (Jun 14, 2013)

RCB are you reading TDS or conductivity?

The conductivity values are about 2X TDS so that's why it looks like your fert rate of 850 mg/L is high.

At 1/2 tsp of MSU or K lite /gal comes to conductivity of about 850 uS/cm. So are you using a full Tsp/gal?

Considering the moss got hit with 2 inches of rain it seems to be holding more TDS than your inter materials. It's still about 10X stronger than the rain water.

What I think is more suprising is the Leca is not that much different. The Leca result indicates that it is also concentrating salts. But which one I can't tell from basic conductivity.


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## gonewild (Jun 14, 2013)

Trithor said:


> What would you say it should be ?



If you are reading ppm the half at around 450ppm would be OK.

All depends on how often you are applying fertilizer.
It won't be consistant to use a strong solution depending on the rain to dilute it... what if t does not rain?


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## gonewild (Jun 14, 2013)

rcb said:


> I've been collecting some TDS numbers over the last month. What do you all think?
> 
> Tap water - 50 - 70ppm TDS.
> 
> ...






> And then one day, after about 2 inches of rain had fallen, I squeezed out spag that was in a pot, 132ppm TDS. (This was suprising as I've always been told that spag "holds" fertilizer salts.)



It is holding salts otherwise after 2inches of rain the reading would be the same as rain water....less than 20



> And at the same time, I set one of my Catts (potted in LECA) in a cup, allowed just enough more rain to fall to collect, and TDS was 98ppm TDS. I should have done this as it was first raining, but couldn't.



The difference between the leca and moss media could just be a result of greater surface in one media.



> Do these make sense? - especially the water collected after rainfall from the pots - I am taking this as the rain does significantly flush the pots.



The rain does flush the pots but of which nutrients?


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## Ray (Jun 15, 2013)

OF COURSE the LECA accumulates minerals. Everything does.

Start with a "pure" clean pellet, and saturate it it with a 50 ppm N solution.

As it dries from the outside in, the solute minerals concentrate, moving more and more to the center of the pellet. Once enough solvent evaporates, the minerals precipitate. Those solids are at a 1-million ppm concentration, and when they are re-exposed to solvent (wetted again), do not instantly redissolve. 

Repeat the process over and over, so the level of accumulation increases.

Add to that any rapid drying due to sun exposure, high temperatures, etc, and the deposits can be closer to the surface.

What gets extracted by the rainwater is entirely a solubility issue at that point. (Which is why I try to keep my S/H pots totally wet at all times - no drying = no precipitation.)


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## rcb (Jun 16, 2013)

The device readout shows ppm, so its ppm.

It sounds strong yes, but I've got no root tip burn, nor any other symptoms of fertilizer burn. It is a total of 4 teaspoons in 20 l of tap water.


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## ALToronto (Jun 16, 2013)

That seems like commercial greenhouse dosage.


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## gonewild (Jun 16, 2013)

The dosage is consistent with commercial growing where plants are forced under optimum environmental conditions.

If you are intending to follow the new er idea of the K-lite nutrition the application is too strong. 

Since you are growing outdoors using rainfall you don't really have much control.


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## Ozpaph (Jun 16, 2013)

I Think my paphs are better with fertilizer diultions about 300+/- and plenty of flushing.
I would use half what you are - depending on media, flushing, frequency etc.


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## limuhead (Jun 16, 2013)

I find it very interesting that many people on slippertalk are very into tds, conductivity fertilizer concentrations, K-lite, testing of all sorts and so on. I feel very fortunate and grateful that all I have to do is throw an orchid in a pot or in my trees and fertilize, spray for bugs, and fungus once in a while. I have gone through testing different fertilizers, media, just about everything and I have found in my experience that location is everything. I honestly don't see much difference from Miracle Grow, MSU, K-lite or any of the other stuff that I have used in the past. The only thing that I have noticed that makes any real difference is lowering the fertilizer concentration in winter and upping it slightly in the summer. You guys must really love your orchids, either that or you're nuts...


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## limuhead (Jun 16, 2013)

and oh yeah, I am watering my plants and posting at the same time, just starting raining here...


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## orcoholic (Jun 16, 2013)

If your TDS meter is calibrated then as a general rule of thumb, 400ppm while the orchid is growing and 200ppm when not, is safe for any orchid.


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## Stone (Jun 16, 2013)

limuhead said:


> I find it very interesting that many people on slippertalk are very into tds, conductivity fertilizer concentrations, K-lite, testing of all sorts and so on. I feel very fortunate and grateful that all I have to do is throw an orchid in a pot or in my trees and fertilize, spray for bugs, and fungus once in a while. I have gone through testing different fertilizers, media, just about everything and I have found in my experience that location is everything. I honestly don't see much difference from Miracle Grow, MSU, K-lite or any of the other stuff that I have used in the past. The only thing that I have noticed that makes any real difference is lowering the fertilizer concentration in winter and upping it slightly in the summer. You guys must really love your orchids, either that or you're nuts...



All probably true but we have nothing else to talk about at the moment:rollhappy:


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## Ozpaph (Jun 16, 2013)

yes we're nuts and all self appointed experts on everything - just ask us!


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## Stone (Jun 16, 2013)

This may stop some confusion:


EC (in dS/m) x 640 = TDS (in ppm)

1 dS/m = 1 mS/m = 1000 uS/m
1 uS/m = 0.001 dS/m.

So EC (in uS/m) x 0.64 = TDS (in ppm)

You should be able to work out anything you want form this with any meter.


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## gonewild (Jun 16, 2013)

Stone said:


> This may stop some confusion:
> 
> 
> EC (in dS/m) x 640 = TDS (in ppm)
> ...



Yep! Now no one is confused at all.


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## rcb (Jun 16, 2013)

Ok, but when I was using 3.5 tsp per 20 l, I was seeing issues. I increased it by 1/2 a teaspoon for 20 l (as recommended on here) and another fertilizing or so a week (as recommended on here), and its too much? What am I missing?

Since I have increased I'm not seeing issues at all. 

As for testing Klite, I'm not trying to prove or disprove anything. I'm just trying to work out a way to grow my plants the best I can in the conditions I have to live with.

I continue to see phenomenal growth and flowering, especially in my Hoyas too. So it does appear, at least to me, that there may be something to this Klite. But if you remember, I think I was seeing some nutritional deficiencies before, so I went with 75/25 blend, still a lot less K than most, but a little higher than straight klite.

I'm also interpreting my numbers a little different than most of you apparently. I found that after rain, the numbers are extremely low, considering they are getting fertilized with 850 ppm and dropping down to 100 ppm after a normal and common rain.


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## gonewild (Jun 16, 2013)

If it works with your conditions nothing else matters.

I think we gave you amounts based on what would not cause any problems.

When you increased the strength of the fertilizer you went over the threshold into a high dose range.

With your rainfall your media is getting flushed well so everything is OK.
But applying fertilizer at 850 ppm is a strong dose until it gets diluted by rain or the next watering. Also at 850 ppm you may be building up reserves of nutrients in the media that are not leaching out.

If your plants are performing well now then all is good. But you asked what we thought about the ppm readings you get so we will tell you!


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## rcb (Jun 16, 2013)

I do have to say its pretty amazing what was to me, very little difference in amount of fertilizer, the difference in the the plants are behaving. In the last month, the 15 Catt alliance plants that have bloomed, not one them is showing any of that nasty reddish color and premature leaf drop.

So yes, as my boys would say, it's all good dude.

Now, I am moving this week to a completely different part of Florida, with completely different conditions, so I'll probably be back in a month begging for advice again 

But the good thing is I will be home more often, so I will be able to do a more daily care of them.


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## ZWUM (Jun 16, 2013)

Ozpaph said:


> yes we're nuts and all self appointed experts on everything - just ask us!



Lol


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## Rick (Jun 16, 2013)

Stone said:


> This may stop some confusion:
> 
> 
> EC (in dS/m) x 640 = TDS (in ppm)
> ...



That 640 constant varies considerably based on the salt composition. For straight NaCl and KCl it would be 500. For heavy sulfate based sytems something else. For heavy nitrogen based systems something else altogether. The only true way to measure TDS is by evaporating down the sample of water and weighing the solid residue. 

The meter only measures conductance (or resistance) and does a similar calculation based on whatever algorithm and salt constant is programed into it.

So you may get a very poor correlation when you actually weigh out some fert and try to check it against a TDS meter.


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## Rick (Jun 16, 2013)

rcb said:


> I do have to say its pretty amazing what was to me, very little difference in amount of fertilizer, the difference in the the plants are behaving. In the last month, the 15 Catt alliance plants that have bloomed, not one them is showing any of that nasty reddish color and premature leaf drop.




Yes you only shifted from the equivalent of 2/3 tsp per gal to 3/4 tsp/gal.

May have also saturated out the binding sites in the potting matrix.

Also being at the mercy of the rain for flushing, its hard to say if your rainfall dropped by the same 13% increase in fert for the last month or so.

Or maybe the plants actually adapted?

But I'm glad your plants are still on track.


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## Ozpaph (Jun 16, 2013)

Rick said:


> Yes you only shifted from the equivalent of 2/3 tsp per gal to 3/4 tsp/gal.
> 
> .



It seems a lot to us metric people who have 4.5l per gallon and not US gallons (??3.55l/gal)


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## Stone (Jun 16, 2013)

Rick said:


> That 640 constant varies considerably based on the salt composition. For straight NaCl and KCl it would be 500. For heavy sulfate based sytems something else. For heavy nitrogen based systems something else altogether. The only true way to measure TDS is by evaporating down the sample of water and weighing the solid residue.
> 
> The meter only measures conductance (or resistance) and does a similar calculation based on whatever algorithm and salt constant is programed into it.
> 
> So you may get a very poor correlation when you actually weigh out some fert and try to check it against a TDS meter.



Yes it is only aprox. and differs with with salt types but most of the general ferts we use are very similar and I have used this for a long while without problem.


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## Stone (Jun 16, 2013)

Ozpaph said:


> It seems a lot to us metric people who have 4.5l per gallon and not US gallons (??3.55l/gal)



Yes its about time the imperial system is relegated to history where it belongs


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## Rick (Jun 16, 2013)

Ozpaph said:


> It seems a lot to us metric people who have 4.5l per gallon and not US gallons (??3.55l/gal)



Its 3.785

But I can round up to 4 if you want to round down to 4:wink:


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## Ozpaph (Jun 17, 2013)

deal!


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