wait until Oldfishlady confirm what i am saying. If you will not have answer from her or anyone else who already knows what is going on then yes i would change the water and put him in epsom salt. It the same preparations. I would really do 3tsp/gall though.
I have a question though did you see anything visible under his scales ? And one more question is his scales raised on all his body or just partially?
The reason i am asking that because i saw the post when fish had external black parasites under the scales and scales were raised. But i am really don't think that he has it just want to make sure.
Because i would think if it fluid in his body then all his scales will be raised. Is it make sense?