So last week I got three Tiger barbs, one Angel fish, one Rainbow shark. I already had an oto and a peppered Cory catfish from a past tank. I decided to restart my 15 gallon. I let the tank cycle for five days before putting the fish in. I added a little aquarium salt for good measure. ADDITIONAL INFO: My pH level is 6.5. I put them in after their bags floated in the water for an hour. I did everything according to procedure. All seem well for a few days until I noticed that one of my tiger barbs had what appeared to be red swollen lips. I thought it had white lips before like the others but then I noticed in a picture I took of the bag when I got them that it had the swollen lips before. It refused to eat. I even tried my freeze-dried blood worms but it wouldn't eat anything. I was worried for him seeing that he was being exiled by the other fish. Just the other night I found him dead. I immediately returned him and brought home another one but it was too late, the disease had spread to my two other barbs. Then that night, I found my catfish dead on the gravel, he was slightly discolored and his lips looked weird. I didn't know what to do. I decided to remove all of the water, disinfect all of my decor and isolate my three tiger barbs. I went to the pet store the next day to take back my rainbow shark (for unrelated reasons), to get new fish, and to ask a worker what to do. He said he had never heard of anything like it but he suspected a bacterial problem. He suggested Melafix. I have giving them the correct dosage for the past couple days and I have seen no change. My tigers seem to be getting progressively worse. What do I do? What type of disease is this? How do I treat? I could really use the help and it would be appreciated. Attached is a photo of the fish when I first got him. He is the one in the top middle. I couldn't find a way to flip it so sorry if it's hard to see.