What is Dropsy?
Fish swells up like a balloon and may show popeyes. It may recover with no treatment and may die despite it. The swelling is because the fish is absorbing water faster than it can eliminate it, and it can be caused by many different problems. High nitrates are one thing to check. Internal bacterial infections, including fish TB, are other possibilities. If there are no water quality problems, you may want to attempt antibiotic treatment in a separate tank.