Originally Posted by nikki_kaiser
If he hasn't added any snails or other live things recently, and his ammonia levels and nitrite levels are at 0, I would look at pH (could be too high or too low), oxygen levels (depletion of oxygen can cause their gills to turn red), test for nitrates, and even use a better quality dechlorinator if he's not already. Do a decent clean up of substrate and filters, and a partial water change.
If you can eliminate water quality or issues, then it sounds like a bacterial infection to be honest.
My science teacher has like 2 oxygen pumps on both sides of the tank so I highly doubt lack of oxygen.
I will confirm his pH and see if its a bacterial infection. What do you advise on for curing bacterial infections?