No don't use all three meds they are what treat velvet, ask the store for a very good velvet med, plus no you can't keep the snail in the tank, sorry.
Treat the whole tank as the fish will all be affected by the parasite as it multiplies fast, and turn temp up to 30, also increase aeration as meds take the 02 out of the water, also high temps takes the 02 out of the water, so aeration is important.
Treat the whole tank as the fish will all be affected by the parasite as it multiplies fast, and turn temp up to 30, also increase aeration as meds take the 02 out of the water, also high temps takes the 02 out of the water, so aeration is important.