Welcome to Aquarium Advice. I am so sorry to hear that Joe is unwell.
Did you recently change his conditions before this happened?
Added anything to the tank?
What is your water care schedule? Do you have a filter and did you recently throw out an old pad or clean it in tap water?
Keeping the water in perfect condition is the first thing to make sure of.
If you haven't done much for water changes recently, I would do a series of water changes to help refresh the water in the tank to be as fresh and good as possible.
Temperature matching his current water, and using water dechlorinator - check if your dechlorinator takes care of Chloramine, as in summers, many times cities use it because it is stronger.
What size tank is it?
So a 20% water change, then about an hour later do another one, and another in another hour. Then wait a few or 8 hours and do that again.
Also check out this article
Also depending on of the water changes seem to help him you might consider
Epsom salt therapy. If the trouble needs antibiotic, then the Epsom salt will not cure him. But it can help with minor body problems and some ability for the fish to help regulate it's system better and help be able to fight off some things.
FW & SW
Favorite tank right now - 72G Bowfront Wadai Tetra, Cardinal Tetras, Ghost Glass Cat Kryptopterus bicirrhis and Clown Loach Cory haven
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
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