Your fish is constipated you say? I'm curious as to how you came up with that? I use Dr. Wellfish's Aquarium Salt, I don't know if it's the same as Epsom salts, you'd have to research that one, but I've always found that using as sparingly (or not at all) is the best policy. Make sure you don't have any snails or scaleless fish in the tank. Some types of plecos are sensitive also, so be careful. Also be sure to take out all plants as it will most definately kill them. Anacharis is the only one I know of to survive and it nearly kills that stuff too.