# Epsom Salt and CaCl2 - Ratios



## Doc7 (Feb 27, 2017)

TLDR: This is not asking what is the optimal ratio. This is a chemistry math problem for how to achieve a 4:1 ratio, regardless of whether or not that's the right or important "goal". Upshot is, historically this board and another have had a lot of math bandied about that show two results, one that Epsom Salt and Calcium Chloride (water content included or not) should be in about a 1:1 weight ratio, and one that shows a 1:2 ratio. Which is right??

There are two very different schools of thought in the mid-2000s on this board, and I can't tell who's math is wrong.

In seeking a target of 6-7 dGH in 43 gallons of 0 dGH water using RotalaButterfly, it tells me that if I use 15 grams of CaCl2 (I'll get into Anhydrous vs Dihydrated in a moment) and 15 grams of Epsom Salt (MgSO4 x 7 H2O:

It will be:
(w/ Anhydrous CaCl2) 33 ppm Ca, 4.6 dGH and 8.5 ppm Mg 2 dGH (total 6.6 dGH)
(w/ di-dhydrate) 25 ppm Ca, 3.6 dGH / 8.5 ppm Mg 2 dGH (Total 5.6 dGH)

The ratio is 3:1 for dihydrate and 4:1 for the anhydrous. So no matter WHAT level of moisture is in my unknown bag of Calcium Chloride, adding 15g each Epsom Salt and CaCl2 PER THIS MATH would be between 3-4:1 Ca/Mg ratio and 5.6-6.6 dGH.* PERFECT water!*

_*Here is the problem!!*_

That math matches up VERY close with this (he calls for 6:7 ratio, I made it easy by saying 15g each):

https://www.plantedtank.net/forums/...osing-calcium-chloride-magnesium-sulfate.html
ThomE, 2005:


> about one gram of mixed calcium chloride and magnesium sulfate (mixed 6:7 by weight) will raise 10 gallons of water by 1 degree general hardness (1 dGH) and provide an ideal calcium to magnesium ratio (3:1)
> by Kevin Zippel, Ph.D


and then again, here, some math on this site. This matches up exactly with a 1:1 ratio.
https://www.aquaticplantcentral.com...p-calculating-correct-dosage-cacl2-mgso4.html


> Short answer: Niko's calc + Fertilator
> 
> Long answer:
> Starting with Mg portion of target:
> ...


Later, in the same thread I linked FIRST above, we have our first detractor. This gentlemen now claims a more than 2:1 Ratio of CaCl2 to MgSO4 is required for the 4:1 ratio. 
Hypancistrus, 2005:


> That's WAY WAY too much magnesium. Most people either do a ratio of 3:1 calcium:magnesium or 4:1 calcium:magnesium.
> 
> The numbers for a 4:1 ratio are:
> 
> ...


And now, in the APC Link above, math that backs up this quote:


> I haven't totally figured out czado's methods but he is incorrect. A degree of German Hardness is equivalent to 10 ppm of calcium oxide (CaO) or 17.86 ppm of calcium carbonate (CaCO3). CaO contains 7.1469 ppm of calcium and 2.853 ppm of oxygen. CaCO3 contains 7.1469 ppm of calcium and 10.7145 ppm of carbonate (CO3). See my work below.
> 
> To raise gH by 1 dgH in 1 gallon of water using calcium chloride dihydrate and magnesium sulfate heptahydrate while maintainig a 4:1 ratio of calcium to magnesium cations:
> 
> ...


So here we have a lot of math, which is ALL from 2005 (though the chemistry hasn't changed! but the posters around here sure have!) where some are saying 1:1 and some are sayin a little bit over 2:1 of these two compounds is what is needed. RotalaButterfly apparently sides with the 1:1s.

What say y'all??


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## Doc7 (Feb 27, 2017)

Using this, non aquatic calculator, it again shows that 33 ppm Ca ions and 8.5 ppm Mg ions leads to a hardness of 6.6 which coincides with the rotala butterfly calculation. (2 is from Epsom Salt and 4.6 from CaCl2).
https://www.lenntech.com/ro/water-hardness.htm

It seems to me that the difference in the two sets of math above is that one is targeting a 4:1 ratio of ppm Ca vs ppm Mg. The other one is targeting a 4:1 ratio of dGH impact. IE for a dGH of 5 they are looking at 1 dGH from Epsom Salt and 4 dGH from Calcium Chloride.

For giggles, I did prove in a bucket that the Epsom Salt impact on GH is correct.


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## hoppycalif (Apr 7, 2005)

There is no perfect ratio of any of the nutrients in water. We need to have enough of each, but the ratio of any two of them is not significant. If you accept that, it gets easier to decide how much of any one chemical you should add to the water. My strong preference is to add nothing to the water that isn't essential for good results. If the water is soft, use soft water. If it is hard, use hard water. Etc. The problem shows up only when your water is extremely soft - almost no calcium and magnesium - or when your water has near zero carbonate hardness - almost no carbonates/bicarbonates in the water. That is a unique situation that few of us ever see.


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## Doc7 (Feb 27, 2017)

hoppycalif said:


> There is no perfect ratio of any of the nutrients in water. We need to have enough of each, but the ratio of any two of them is not significant. If you accept that, it gets easier to decide how much of any one chemical you should add to the water. My strong preference is to add nothing to the water that isn't essential for good results. If the water is soft, use soft water. If it is hard, use hard water. Etc. The problem shows up only when your water is extremely soft - almost no calcium and magnesium - or when your water has near zero carbonate hardness - almost no carbonates/bicarbonates in the water. That is a unique situation that few of us ever see.


That's right, Mine is 0 KH 0 GH.

But hoppy - my question isn't so much "whats the perfect ratio?"

It is a math question. Is adding Calcium Chloride and Epsom Salt in a 1:1 Ratio equivalent to a 4:1 Ca/Mg Ratio, or is adding Calcium Chloride and Epsom Salt in a 2:1 Ratio equivalent to a 4:1 Ca/Mg Ratio? There are many posts on TPT and APC that say "yes" to either one.

Thank you,


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## mistergreen (Mar 3, 2007)

Look at the molar mass for you calculation.
MgSO4 is 120 g/mol, Mg is 24 atomic weight
CaCl2 is 110g/mol, Ca is 40 atomic weight

So Ca is close to double of Mg (by weight) given the same weight in MgSO4 & CaCl2. No need to do calculations, just look at the numbers.
In the end, it's just close to 1:1 in numbers of atoms.


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## Doc7 (Feb 27, 2017)

mistergreen said:


> Look at the molar mass for you calculation.
> MgSO4 is 120 g/mol, Mg is 24 atomic weight
> CaCl2 is 110g/mol, Ca is 40 atomic weight
> 
> ...


More than 50% of the weight of MgSO4 in Epsom salt is tied up in the 7 H2O molecules also right?

So the double Calcium in same weight of pure product and then another double from the H2O weight brings us to 4:1?


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## mistergreen (Mar 3, 2007)

Ok, 
MgSO4.7H2O is 120 + 126g/mol = 246g/mol
CaCl2 is 110g/mol

So, you do have about 2:1 Ca:Mg for the same weight.


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## mistergreen (Mar 3, 2007)

Oh, just realized CaCl2 is usually hydrates too.. CaCl2(H2O)x : x= 0,1,2,4,6

Let's just say it's a 1:1 to 2:1 ratio for simplicity.


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## Doc7 (Feb 27, 2017)

I’m not getting what you’re getting after. Using Calcium Chloride Dihydrate and Epsom Salt RotalaButterfly says 3:1 in a Ppm (mg/L) ratio. With anhydrous it is 4:1.

I will write it out when I get back to house but not seeing how you are getting 2:1 or 1:1. You already had double above (Ca being double the percent weight of compound as Mg is in its compound) and adding more water to Epsom salt (7 H2O) weight and less to calcium chloride (typically 2 or 0) only makes the ratio go even higher than 2:1.


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