Planted Tank Obsessed
Join Date: Jan 2008
Location: Sioux Falls, SD
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.