Epsom Salt and CaCl2 - Ratios - Fertilizing - Aquatic Plant Central

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Old 04-29-2020, 06:54 PM   #1 (permalink)
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Default Epsom Salt and CaCl2 - Ratios

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/1...m-sulfate.html
ThomE, 2005:
Quote:
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/...cl2-mgso4.html
Quote:
Short answer: Niko's calc + Fertilator

Long answer:
Starting with Mg portion of target:
Ca ppm = 4 x Mg ppm
(2.497 x Ca ppm) + (4.119 x Mg ppm) = GH ppm
9.988 Mg ppm + 4.119 Mg ppm = 17.9 ppm
Target Mg ppm = 1.27
Target Ca ppm = 5.08

MgSO4+7H20 dose (note: using 55gal, but you should substract 15-20% for displacement if you are anal):
Target Mg ppm x 3.77L/gal x (mg MgSO4+7H2O4)/mg Mg x Tank gal = MgSO4 mg dose
1.27mg Mg/L x 3.77L/gal x (10.1mg MgSO4+7H2O4)/mg Mg x 55gal = 2660mg MgSO4 =~ 2.7g MgSO4

CaCl2 dose:
Target Ca ppm x 3.77L/gal x mg CaCl2/mg Ca x Tank gal = CaCl2 mg dose
5.08mg Ca/L x 3.77L/gal x 2.77mg CaCl2/mg Ca x 55gal = 2917mg CaCl2 = ~ 2.9g CaCl2

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:
Quote:
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:

For 1 dGH per gallon - 0.07939 grams CaCl2*2H2O, and 0.03327 grams MgSO4*7H2O (epsom salt).

So, to raise 50 gallons by 5 dGH, you want 19.85 grams of CaCl2*2H2O and 8.32 grams of MgSO4*7H2O.

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

- Add 0.07939 grams of CaCl2*2H2O
- Add 0.03328 grams of MgSO4*7H2O

For 55 gallons, this would be 4.37 grams CaCl2*2H2O and 1.83 grams of MgSO4*7H2O.

Use this as a starting point. There are other factors that will affect the actual gH reading - calcium and magnesium cations may not register 100% equally on your test, the quality of the compounds used (agricultural grade from Greg Watson vs. reagent ACS grade from a lab supplier), compounds in your specific water chemistry - so simply adjust the measurement by using the same percent of each. (Example, if it raises it a bit more than you wanted, try multiplying each measurement by .75 to dose at 75% strength next time.)

DO NOT DISSOLVE CaCl2 and MgSO4 IN THE SAME CONTAINER! - The calcium and sulfate ions will bind and calcium sulfate will precipitate out. Calcium Sulfate is "insoluble" - it will dissolve but verrryyy sloowwllly.


-------------------------


Calculations - Assumes an EDTA chelation gH test in which calcium and magnesium cations register equally


- Calcium = 40.078 g/Mole

- CaCl2*2H2O Dihydrous Calcium Chloride = 147.01396 g/Mole

- Magnesium = 24.305 g/Mole

- MgSO4*7H2O Heptahydrate Magnesium Sulfate = 246.47556 g/Mole


1 dGH (Degrees of German Hardness) for calcium = 7.14691 ppm or mg/Liter / 1000
= .00714691 g/Liter / 40.078 g/Mole = .00017832 Moles

1 dGH (Degrees of German Hardness) for magnesium:
.00017832 * 24.305 = .0043342 g/Liter * 1000
= 4.33419 mg/Liter or ppm


Increasing 1 dGH of Calcium (7.14691 ppm) in 1 liter of water using Dihydrous Calcium Chloride:
7.14691 / (40.078 / 147.01396) = 26.21626 mg/Liter

Increasing 1 dGH of Magnesium (4.33419 ppm) in 1 liter of water using Heptahydrate Magnesium Sulfate (Epsom Salt):
4.33419 / (24.305 / 246.47556) = 43.95274 mg/Liter


Converted to Gallons:

Increasing 1 dGH of Calcium in 1 gallon of water using Dihydrous Calcium Chloride:
26.21626 * 3.785412 = 99.23934 mg/Gallon

Increasing 1 dGH of Magnesium in 1 gallon of water using Heptahydrate Magnesium Sulfate (Epsom Salt):
43.95274 * 3.785412 = 166.37924 mg/Gallon


Converted to a 4 : 1 ratio of calcium : magnesium

99.23934 mg/Gallon CaCl2 = 1 dGH
166.37924 mg/Gallon = 1 dGH

79.39147 mg/Gallon = .80 dGH
33.27585 mg/Gallon = .20 dGH



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??

Last edited by Doc7; 04-29-2020 at 07:07 PM..
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Old 04-30-2020, 07:37 AM   #2 (permalink)
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Default Re: Epsom Salt and CaCl2 - Ratios

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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Old 04-30-2020, 08:40 AM   #3 (permalink)
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Default Re: Epsom Salt and CaCl2 - Ratios

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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Old 04-30-2020, 08:45 AM   #4 (permalink)
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Default Re: Epsom Salt and CaCl2 - Ratios

Quote:
Originally Posted by hoppycalif View Post
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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Old 04-30-2020, 09:51 AM   #5 (permalink)
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Default Re: Epsom Salt and CaCl2 - Ratios

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.

Last edited by mistergreen; 04-30-2020 at 10:43 AM..
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Old 04-30-2020, 11:37 AM   #6 (permalink)
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Default Epsom Salt and CaCl2 - Ratios

Quote:
Originally Posted by mistergreen View Post
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.

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?

Last edited by Doc7; 04-30-2020 at 11:57 AM..
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Old 04-30-2020, 01:22 PM   #7 (permalink)
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Default Re: Epsom Salt and CaCl2 - Ratios

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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Old 04-30-2020, 05:33 PM   #8 (permalink)
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Default Re: Epsom Salt and CaCl2 - Ratios

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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Old 05-01-2020, 10:14 AM   #9 (permalink)
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Default Epsom Salt and CaCl2 - Ratios

Iím not getting what youíre 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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