Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Equilibrium has calcium and magnesium, so if the GH originally has a reasonably balanced ratio of Ca:Mg, then the Equilibrium is a good idea.
If you think the Ca:Mg ratio is somehow skewed so the Mg is too low, then Epsom salt will add just the Mg without the Ca. This might be the way to go, seeing the water quality report shows so little Mg.
Plants use Ca and Mg in a ratio of about 4 parts Ca to 1 part Mg. The water does not have to have this exact ratio, but something close to it would be pretty good.
If you get a calcium test for aquariums then look for the formula to figure out how much Ca and how much Mg is in your water you could get a better idea how to best supplement your tank. The math is easy enough, but it is not simply GH-Ca=Mg. Look it up.
You know, even easier is to dose and watch the plants.