His tail was already curly when I got him from the fish shop. His activity, feeding and behaviour were all as per normal for the past 2 weeks despite the sores on his body. It is only the last 2 days that he became listless.No ammonia and nitrites, I did not test for nitrates. Tank mates are 1 ranchu, 1 oranda, and 3 corydoras in a 55G tank. I bought him from the same fish shop a year ago as the 2 other goldfishes. The other fishes are all ok. The tank is filtered by a fluval filter at 700L/HR. Water changes 50% once a week. They are all on Hiraki sinking pellets and peas trice a week.