Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If the stores near you are on the same water system, and have kept the fish in the store for perhaps a week, then the fish will probably be OK in your tank with your tap water.
Adding Epsom salt is not really the proper answer to raising the GH.
GH is a measure of both Ca and Mg. Fish and plants need both.
When you use Epsom salt you are only adding Mg.
To properly raise the GH use a combination of minerals that include both Ca and Mg, in the right ratios.