My common goldfish had developed a few red sores on the side of its body. But after the addition of aquarium salt and Melafix, it cleared. However, a week for so afterwards, the skin there looks like its rotting. Its not red or anything and I dont see any parasites living on it. The scales look like theyre coming off.

The fish still has its normal eating habits, no clamped fins, no sitting at bottom of tank. All behavior is normal except that a part of its side belly looks like its rotting away. ._. what do I do and what is it?