# Magnesium nitrate vs epsom salt



## papheteer (Mar 19, 2014)

What is better for paphs? And why? Thanks!!


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## NYEric (Mar 19, 2014)

Which one don't you have? That will be the better one for sure!


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## Ray (Mar 19, 2014)

That's like asking "which is better for me, chicken or broccoli?" - they are different chemistries that will have different effects on the plant.


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## papheteer (Mar 19, 2014)

Let me rephrase my question. If my purpose is to supplement magnesium to my paphs, what's more efficient (better absorption) between the two?


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## gonewild (Mar 19, 2014)

It should not matter. Magnesium is Magnesium. 
With the magnesium Nitrate you also have to consider the Nitrogen that is added.
With Epsom salts you have added sulfur.


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## papheteer (Mar 19, 2014)

Thank you Lance. It's a bit easier to deal with magnesium nitrate as I can make a concentrate with Calcium nitrate and not get precipitation.
So I guess I'll use it.


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## Trithor (Mar 20, 2014)

Just be very careful of the N ppm with the final dilution. I have been using this at very dilute levels to supplement my Ca and Mg as our municipal water is deficient in both, since starting it at the beginning of the season, there has been a definite improvement in the appearance of my plants.


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## TyroneGenade (Mar 20, 2014)

I don't like adding sulfates. They are bad for the environment and soil bacteria can turn them into toxic H2S under anaerobic conditions.

Ca:Mg should be somewhere around 3:1. You can make a concentrated solution of Ca & Mg of this ratio using a little chemical no-how. 

Ca2+ sulfate is poorly soluble. So, if you add MgSO4 to Ca(NO3)2 you will precipiate some of the Ca as CaSO4 but be left with concentrated Ca/Mg(NO3)2. The above ratio is mass-mass. Of 100 g of anhydrous Ca(NO3)2, about 24 g is Ca. So, for every 100 g of Ca(NO3)2 you want to add about 8 g of Mg. Mg is 9.7% (m/m) of epson salts, so you would need to add 83 g of epson salt to the 100 g of calcium nitrate. 

Now, this is where the problem comes in: do you have anhydrous calcium nitrate or the tetrahydrate? If the latter, then the math changes. Ca is only 17% of the mass of 100 g of the tetrahydrate salt so each 100g would be 17g of Ca. To this you would need to add about 5 g of Mg or 63 g of epson salts.

You will get a CaSO4 slurry at the bottom of the bottle. Just ignore it and use the clear liquid above. It should be about 3:1 Ca:Mg. You would still add small amounts of sulfates to the plants but that isn't much to worry about... The plants need a little sulfur.


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## papheteer (Mar 20, 2014)

Tyrone thanks for the explanation. The calcium nitrate I got from a local hydroponics store is the prill type. That's all I know about it. 

Looks like this:
http://www.amazon.com/gp/aw/d/B007GQ0E8E#immersive_view?1395347626694


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## Ray (Mar 20, 2014)

Assuming it's normal horticultural grade like I sell, it's 15.5-0-0-22 Ca


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## gonewild (Mar 20, 2014)

If it is the prill type it has a wax coating. When you dissolve it in water the wax will float to the surface. Makes a little mess but does not hurt the plants. But if you use an injector or fine nozzle it might plug it up.
Easy to filter off the wax. Dissolve the prills in a small amount of water and then pour the solution through a cotton cloth. The wax fill be trapped in the cloth. I actually pour it through a strong paper towel.


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## papheteer (Mar 20, 2014)

Nope. The type I got doesn't have wax coating. Dissolves completely in seconds.


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## Rick (Mar 20, 2014)

TyroneGenade said:


> I don't like adding sulfates. They are bad for the environment and soil bacteria can turn them into toxic H2S under anaerobic conditions.
> 
> .



Nitrate is a lot more toxic in the environment than sulfate.

Natural background concentrations of sufate are often 100 to 1000ppm.

Nitrates are generally less than 5 ppm in aquatic systems, and greater than 20-40ppm (as N) start causing chronic toxicity effects to fish and inverts.

The H2S happens under such anaerobic conditions (deep rotten sediment) that only specialized life forms can exist in that envronment anyway. You need at least a few ppm of O2 to support normal aquatic life (and then no H2S formation anyhow).

I would play with epsom salts long before messing with mag nitrate. Or if you really want to add a few ppm of Mg then use magox and neutralize with phosphoric acid (for a Mag Phosphate solution).


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## Rick (Mar 20, 2014)

papheteer said:


> Let me rephrase my question. If my purpose is to supplement magnesium to my paphs, what's more efficient (better absorption) between the two?



How much are you planning on adding.

As Tyrone pointed out you shouldn't add more than what you have in Calcium. (I think you could go to 1:1 ratio if you really want to push it for a while).

So do you know how much soluble Ca is in your system?

If you are just trying to squirt a few ppm of Mg into your pots then make a a weak 5ppm (as Mg) solution of epsom salts and be done with it. That would carry 20ppm of SO4 which is lower than whats in most tap water nationwide.


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## papheteer (Mar 20, 2014)

Rick said:


> How much are you planning on adding.
> 
> As Tyrone pointed out you shouldn't add more than what you have in Calcium. (I think you could go to 1:1 ratio if you really want to push it for a while).
> 
> ...



Rick right now my tap water has 33 ppm calcium and 8 ppm magnesium but they are carbonates. I don't know how readily absorbed carbonates are. I wanna supplement with 40 ppm calcium and 20 ppm magnesium (on top of what I have in my tap water) once or twice a month.


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## Rick (Mar 20, 2014)

papheteer said:


> Rick right now my tap water has 33 ppm calcium and 8 ppm magnesium but they are carbonates. I don't know how readily absorbed carbonates are. I wanna supplement with 40 ppm calcium and 20 ppm magnesium (on top of what I have in my tap water) once or twice a month.



Actually they are not as carbonates, but the hardness measures are mathematically based on an expression of carbonates.

Calcium carbonate is basically insoluble until below pH 2. So unless you see chunks of rock in your water, and you are not drinking acid, then your Ca and Mg are soluble. Depending on the alkalinity of your material there are theoretical ion pairs of calcium and magnesium bicarbonate. And your water will also have Na, K, SO4, and chloride. 

Most natural surface waters will be mostly salts of calcium and magnesium with sulfate and chloride as the predominant anions. The mix varies around the world. Some places have higher sodium. If you have high bicarbonate ion then the pH will run >9.0 unless under pressure, and then you'd be talking about something like Perrier water (which still has plenty of sulfate and chloride) which will fizz when you pop the top.

Your city water (by law) should have regular analysis results free to the public. They are often available on line from the local health department or water provider. If you are on a well, you are on your own.

If your water report is showing 33 ppm Ca (not "Ca hardness of 33ppm as CaCO3") then you have 33ppm of soluble Ca free to good home. If your report says Ca of 33ppm as CaCO3) then you have 13.3ppm of soluble Ca.

Mg hardness can also be reported as ppm CaCO3, but the conversion to Mg ion concentration is divide by 4.11 instead of 2.48 for Ca.

Post your water report and I can assess it for you.


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## papheteer (Mar 20, 2014)

Hey Rick here's my tap water analysis:

http://www1.toronto.ca/City Of Toro...D/DrinkingWaterAnalysisSummary_2012_FINAL.pdf

Thanks for all the help.


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## TyroneGenade (Mar 20, 2014)

My experience with sulfate is from planted aquariums where it tends to accumulate and cause problems in the substrate or filter (in SA this could be a blessing as it precipitates the cadmium and uranium salts leaching out of the mines!). So, I defer to Rick's sounder (and less labor intensive) advice. 

The amazon Ca nitrate has more water than the tetrahydrate meaning you have a lot less Ca there than before. Ca is only about 12% or 12 g per 100 g. So you would need 4 g of Mg or 41 g of MgSO4.


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## Rick (Mar 20, 2014)

Ok

Ca = 34.7
Mg = 8.7
Na = 14.2
K = 1.5

SO4 = 27.5
Cl = 25.9
HCO3 = 108 (alkalinity of 89 X1.22)

Total N is very low (because its the law for drinking water)
P is 0.

This water would be fine straight up for regular use with a dab of N and P.

You might want to investigate the use of struvite (amonium magnesium phosphate). But I've found that material hard to dissolve.

Adding a few ppm of MgNO3 wouldn't hurt. It might be expensive, but a kilo would probably last you 100 years.

You could also try making that MgPO4 mix I use (milk of magnesia, magox neutralized with phosphoric acid) and a tiny dash of ammonium nitrate.

But I stress tiny. You only need to add 5-10 ppm of N and 1ppm of P


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## Ray (Mar 21, 2014)

gonewild said:


> If it is the prill type it has a wax coating.



Lance, I see no such residue in the material I have.

The prill form of the material indicates that is has been spray dried, nothing more. Certainly it is possible a binder is added to give the prills a bit more structural integrity for handling, but I don't believe it's absolutely necessary.


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## gonewild (Mar 21, 2014)

At least on the west coast a wax coating is added to facilitate getting the calcium nitrate into the ground. The wax slows the atmospheric moisture absorption and allows the nitrate to run through the mechanical priller.

A few times I ordered small amounts of Calcium nitrate from ebay and it came in that form.


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## DavidCampen (Mar 21, 2014)

gonewild said:


> At least on the west coast a wax coating is added to facilitate getting the calcium nitrate into the ground. The wax slows the atmospheric moisture absorption and allows the nitrate to run through the mechanical priller.
> 
> A few times I ordered small amounts of Calcium nitrate from ebay and it came in that form.



I think that the discussion is about magnesium nitrate but, in either event, if you purchase "greenhouse grade" material it is sold to be suitable for dissolving in tanks before application, not spread on the ground. If you do not purchase "greenhouse grade" material then this material is likely to be much less water soluble.

These are greenhouse grade materials:
https://customhydronutrients.com/index.html/download/Magnisal.pdf
http://www.jrpeters.com/Products/Specialty-Nutrients/Buy-Specialty-Nutrients.html


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## Ed M (Mar 23, 2014)

I buy the wax-coated calcium nitrate as well. I merely dissolve it in hot water first and the wax floats to the surface of the water and it will adhere to a paper towel. If you buy a quantity of the non-wax coated calcium nitrate it tends to pull moisture out of the air turning it into a solid block of crystals.


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