I just got over something that sounds the same. One tank (after a friend brought me 10 albino aneus) got fin rot and ich in a bad way. I treated with salt and increased temp (85F). Boosted the aeration to compensate for the increased temp. I treated the fungal problem with malachite green. The fungal infections cleared up but, I was still losing fish. I snipped some gill tissue from the latest floater and found alot of bacteria in the tissue. This didn't concern me too much since the gill from a necropsy. However, I also noted areas of necrosis and atrophy of the edges of what should have been viable tissue. I don't have a means to culture out a sample so, I have no way of proving whether the bacteria are gram-neg or gram-pos. So, I began a 10 day treatment regimen with tetracycline (for both gram-neg and gram-pos) for a bacterial infection secondary to the fungal infestation and the fish cleared up and perked up and the tank stopped suffering losses.