So my brother keeps a betta in a 3.5 gallon heated and filtered tank. He was the one caring for the fish. He feeds omega one betta food. He is supposed to do 75% weekly water changes. I am not sure if he was sticking to the weekly water changes. I asked him weekly and he always said he was about to do the water change so I'm not sure if he did them or not. 2 weeks ago I went in his room to talk to him and I noticed the Betta had pretty bad fin rot and was breathing heavily at the bottom of the tank. I am now in charge of water changes for the fish. For a week and 2 days I did large daily water changes with aquarium salt for the fin rot. The fins seem to have started healing. Unfourtunatley, the Betta is still staying at the bottom and breathing heavily. He still eats each morning when I feed him. I am keeping the 75% daily water changes now without any salt for a few more days. I'm not sure really what's wrong with the Betta. I am guessing it is either ammonia or chlorine burns since those are the only 2 things I could think of. How can I help the Betta? I know my brother loves the Betta and he's really worried about him. I am going to be taking care of the Betta now to make sure his water changes get done. Thanks in advance.