It’s been roughly a week, but has been growing almost like a bubble... it actually ruptured tonight and isn’t looking good... it seemed like fluid came out and now is like a deflated balloon... fish is swimming poorly. Did a 30% water change and added melafix... praying for the best.How long has it been there? You may need to get a hold of a vet as they can excise with anesthesia if needed.
Thank you. Will order and treat if he makes it through the night.Doesn’t look like hith but could have been an abscess that’s grown and it drained. Get some abx like triple sulfa. This should help and it will destroy your biological filter so need to keep an eye on the water quality.