[hoppycalif]

Aragonite will add carbonates to the tank, as well as calcium, so it will gradually raise the KH until it is too high for the fish to do well. If you are willing to do weekly 50+% water changes you can control the rise in KH and the aragonite would be ok.

Seachem Equilibrium is one way to raise the GH, which is calcium and magnesium. Another way is to dose Calcium chloride and Magnesium sulfate (Epsom salts). Neither of those will raise the KH.

 

[hoppycalif]

Epsom salts from the corner grocery store are as good as anything you get from an online fertilizer store, but I found the corner store charged quite a bit more. Since I was ordering other fertilizers I just ordered the MgSO4 too.

 

[hoppycalif]

Calcium sulfate would work fine, except for being slower to dissolve. The advantage of it is that plants use some sulfur, where the chlorine in the calcium chloride would just be along for the ride.