I am currently treating my 20g tank because one fish has fin rot. Yesterday I was at LFS and he said I should not treat the whole tank because it kills off the good bacteria. Which I knew but I thought I had no choice. He suggested buying a 5g and use it as a hospital tank whenever I need it. I told him that I was afraid to put a sick fish in an uncycled tank. He said that you just fill a hospital tank whenever you need to use meds and change about 50% of the water daily before you add the meds. That way the ammonia and nitrites don't build up and the fish should only be in there for about 10 days during the treatment. He said that is how a lot of experienced fish keepers do it. I really like LFS and this guy (the owner) has never steered my wrong. I don't want to set up a permanent hospital tank so this seems like a good solution but I'm still worried. Does anyone else use an uncycled hospital tank just for medicating sick fish???