What Mg do you use?

[DrZoidburg]

I trust my math. The old recipe calculator they used was different cups amounts before they switched to pharma. The new 6 cups. 5.25 :2 cup recipe 1015 grams chloride dihydrate, 493g sulfate heptahydrate. Would be the 5.25 : 2 To get the calculator to work with that cup recipe and get desired ppm. So 5.25/8 = .656 ok now look at molar mass Mg dihydrate vs heptahydrate 131.24096 g/mol divided by 203.30208 g/mol = .6455. I have more math supporting this I just have to find it.

 

[Randy Holmes-Farley Verified Community Expert]

I trust my math. The old recipe calculator they used was different cups amounts before they switched to pharma. The new 6 cups. 5.25 :2 cup recipe 1015 grams chloride dihydrate, 493g sulfate heptahydrate. Would be the 5.25 : 2 To get the calculator to work with that cup recipe and get desired ppm. So 5.25/8 = .656 ok now look at molar mass Mg dihydrate vs heptahydrate 131.24096 g/mol divided by 203.30208 g/mol = .6455. I have more math supporting this I just have to find it.

Well, volume varies by the bulk density of the exact product, but the current calculator for magnesium at BRS via mass (grams) exactly matches the calculator developed for magnesium chloride hexahydrate.

The math is perfectly simple and we can work it out manually if you really want.

 

[Randy Holmes-Farley Verified Community Expert]

Here's the math...

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pick "dry" magnesium chloride and "new pharma pouch"

raise 100 L by 100 ppm magnesium requires 83.3 grams

But we also know that to boost 100 L by 100 ppm (mg/L) magnesium requires 100 L x 100 mg/l = 10,000 mg = 10 grams.

This, the "dry magnesium chloride" in the BRS calculator must be 10/83.3 = 12.0% magnesium by weight.

magnesium weighs 24.3/ g/mole
Magnesium chloride hexahydrate weighs 203.3 g/mole and is thus 11.95% magnesium by weight
magnesium chloride dihydrate (if such a thing existed; it is not commercially available that I have ever seen) weighs 132.3 g/mole and is thus 18.4% magnesium by weight.

Consequently, it is clear that the BRS calculator is assuming the material is magnesium chloride hexahydrate

 

[DrZoidburg]

I realize my mistake. I mixed my diy recipie with calculator math, and am missing a few pages in between somewhere honest. Mixing stuff up. I am familiar with how to get these numbers. I was going off old own diy recipe to match current 7.25 cup one to get the same Mg/L results of Mg, Cl2 and S04 but mine was higher in Cl2 while still matching calculator. At the same time assumed it was dihydrate. I think just 20% more potent is theirs. Every time I dose I account for that. I have 2 gallons of solution left I'd like to find that missing part so I don't have to write it all over again.

 

[Randy Holmes-Farley Verified Community Expert]

I realize my mistake. I mixed my diy recipie with calculator math, and am missing a few pages in between somewhere honest. Mixing stuff up. I am familiar with how to get these numbers. I was going off old own diy recipe to match current 7.25 cup one to get the same Mg/L results of Mg, Cl2 and S04 but mine was higher in Cl2 while still matching calculator. At the same time assumed it was dihydrate. I think just 20% more potent is theirs. Every time I dose I account for that. I have 2 gallons of solution left I'd like to find that missing part so I don't have to write it all over again.

FWIW, BRS uses my DIY recipe for their two/3 part, including the magnesium part:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com

 

[DrZoidburg]

FWIW, BRS uses my DIY recipe for their two/3 part, including the magnesium part:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com

I realized after the fact exactly what I did wrong trying to decipher chicken scratch writing from over 3 years ago missing a few pages. 5 mol hepta 1015 grams, 7.73 mol di = 1015 also. I pulled one set of numbers from another page on accident. Mine was the one ended up 20% stronger. Its worth it because I have went a good amount of time on the same purchase, and still have many more gallons I can make for less than 30$ total Roadrunner, and plain epsom salt. Also thanks randy if at first I wasn't so sure you were wrong I wouldn't of been scrambling old papers for an answer. I know you've done that too?