I would consider doing the Epsom salt treatment first before rushing off to get medications for parasites or bacteria infection. You have stated he is doing better - lets give him some more time before you bombard an already weakened body with heavy medicine.. in my opinion only.
Clean water, food, Epsom and he is doing better you say... you don't know the last time he had eaten, so not seeing any waste from him isn't a surprise. The clear thing could of been excess body slime due to bad water quality.
Not saying it couldn't be either of those stated.. guess an update is needed to know for sure how he is doing and what would be best for him.