I have a 55 gallon tank that is about 6 or 7 years old. My featherfin catfish has a couple white spots on his belly. I'm thinking it might be fungal because it doesn't really look like the pics of ich that I've seen. I haven't introduced anything new to the tank in several months. The other fish seem healthy with no signs of spots on them. The nitrates are 20, ph is 7.8, and ammonia is 0. He has had spots like this before and treating with Pimafix and Melafix for a week cleared it up. This time it's not working. Today was the 6th day of treatment. I was hoping to add a couple bamboo shrimp to my tank so I don't want to use any treatments that might harm when I introduce them after this is cleared up. Does anyone have any advice to what this might be and what I should do about it?