Hi (again!). If you haven't seen any of my posts, we rescued two goldfish from a fair about 4 weeks ago. They were just transferred to a 20 gallon (I know they will need bigger later) due to high ammonia in previous, way to small tank (one guy has healing ammonia burns). We are trying to cycle the tank, but one of my fish was just sitting at the bottom, or hiding in the cave, gills moving fast, not really swimming, fins clamped, and not eating. This morning, his fins were open, but still sort of just hanging without moving much. We did a 50% (approximate) water change - and he's much happier, swimming and chasing his tank-mate. The 20g tank was just set up on Thursday, water parameters are good. I noticed this afternoon that he has a bit of fin rot, at this time, I can't tell if my other fish (the one with healing ammonia burns) has it as well. Can we treat him in the tank with his tank-mate? We have a bottle of Melafix and Tetra Lifeguard - nothing has been put in yet because I don't want to do the wrong thing. Both call for removing the carbon from the filter - this concerns me as they are so messy, and I would assume it wouldn't be good to do any water changes? I have also read that just consistently changing water will help as well. Sorry for all the questions over multiple posts - I just want to give them the best care possible.