Help with epsom salt from Walmart - The Planted Tank Forum
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post #1 of 5 (permalink) Old 03-06-2008, 07:05 AM Thread Starter
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Help with epsom salt from Walmart


I bought some Epsom salt (Magnesium Sulfate) from Walmart, manufacturer by Aaron Industries, it seems that not all Epsom salt are the same because I've seen something on the internet that has different percent in the Guarantee Analysis. Something like 16% Mg.

According to the label on the box, it says:

Guarantee Analysis:
Magnesium (Mg): 9.87% (9.87% Water Soluble Magnesium)
Sulfur (S): 12.98% (12.98 combined Sulfur)
Derived from magnesium sulfate.

Can someone please help me to determine how many gram of this stuff to raise 1 ppm of Mg in 10 gallon?

Thank you.

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post #2 of 5 (permalink) Old 03-06-2008, 01:42 PM
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Hey Kevin - another Kevin here.

So 1ppm Mg = 1milligram of Mg per liter. (unless you mean 1ppm GH - that would be a different calculation)

10 gallons= 37.8 liters, so 1mg/L means you need to add 37.8mg of Mg.

37.8mg of Mg / 0.0987 (fraction Mg in Epsom salt) = 383mg of Epsom salt

383mg = 0.383g of Epsom salt to raise a 10gallon tank by 1ppm Mg

What you have there is true Epsom salt - magnesium sulfate heptahydrate (MgSO4*7H2O).



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post #3 of 5 (permalink) Old 03-06-2008, 01:53 PM
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I should be able to do this so here goes:

1 gal=3.785412 L, so your tank is 37.85412 L
1 ppm=1 mg/L, so you want 37.85412 mg of Mg
Using the percent Mg you gave above, 37.85412mg/0.0987=383.5 (rounded) mg or 0.3835 g of Epsom Salts.

I can't give you any help with converting that to a volume like a teaspoon, but maybe someone else can.

A couple words of caution though, that caculation was for 10 gal of H2O, not a 10 gal aquarium which usually contains less that 10 gal of H2O. Also, it's been a while since I've had to do this, and even though I would go ahead with it, I'm taking no responsibility if you decide to use this. I would wait for confirmation from somebody else to see if they agree with my calculation.

Edit: Looks like somebody else was faster, but I'm glad to see they agree.
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post #4 of 5 (permalink) Old 03-06-2008, 05:49 PM
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here's a calculator

for really small amounts, it's best to make a solution so it's easier to does precisely if you don't have a fancy scale that is..

But it's not a big issue to get the measurements precisely for MgSO4.

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post #5 of 5 (permalink) Old 03-06-2008, 06:05 PM Thread Starter
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Thank you all for your help.
I can't believe how cheap this stuff is! around $0.50 per pound! and that was why I was a bit concern that I might not getting true epsom salt

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