mg or ca

I think I did the exact wrong thing, using epsom salts for mg. Probably didn't need to- and overdoing it could be harmful? I finally got a GH/KH test kit. My general hardness is 10, which I think means there's enough mg and ca in the water supply already- I should have figured as much, since I always have hard water residue on things. So what I had guessed was mg deficiency is probably a symptom of something else. This applies to my other tank as well. It's more likely I need to add calcium (the snail shells look eroded on their ends). Not sure. Well, the big wc I have to do this week after dosing meds will take out the extra mg I hope. Then I can figure it out.

The kH reading was 5- I read a bunch of articles and posts about gH and kH but still don't really understand what these numbers mean for my tank.

My big crypt wendtii looks greener with the lights off. If something's wrong in the tank balance, this plant seems to be showing it. Are crypts are more sensitive than the other plants in some way.