Alright, so on Mother's day we took my mom to an aquarium shop. As we were looking around, I noticed a HUGE goldfish in a tiny tank. Upon looking closer, I could see that he had almost no fins, and was being picked on relentlessly by all the other little fish in the tank (There were also 'freshwater' eels in the tank. o.o..) Anyway, the store owner said that he had been dropped off like that, and offered to give him to us for free. We took him home, and after some time in QT, he went up into the 55g with mom's other goldies. First week he was doing okay despite his lack of fins, but then he started to contract into an arc (as shown in photos) and remain like that. Dad moved him to a QT tank again, and he's been this way for about two weeks now.
It's breaking my heart seeing him like this, because all the while, his fins are growing back, and he still has to wiggle over and beg for food from anyone passing by. I know that dad has tried salts and petstore cure-all stuff, but nothing seems to be working. I can't say he's getting worse, because he looks the same as when it first started-- Just contracted, but no horrible gasping, pineconing, he's eating, and alert.
Does anyone know what could be wrong, or how to treat this?