How is the stress level in the tank?
What is the full stock list?
Was the fish eating in QT?
Any reclusive behaviour?
For now, I would add epsom salt to the tank at 1 cup per 100G - dissolve it in some tank water first. This is a good preventative for bloat, but if a fish is already infected, it won't change things. This will buy you some time to closely observe the tank and determine what is going on.
What is the full stock list?
Was the fish eating in QT?
Any reclusive behaviour?
For now, I would add epsom salt to the tank at 1 cup per 100G - dissolve it in some tank water first. This is a good preventative for bloat, but if a fish is already infected, it won't change things. This will buy you some time to closely observe the tank and determine what is going on.