How long does it usually take to see healing in a fish with fin rot? I started medicating my betta 3 days ago. The medicine says not to do a water change until after 7 days of using the meds, and then the process can be repeated if necessary. I was just wondering how long it should take until I see Cobalt improving. (I am using BettaFix) He is acting fine, but his tail looks kinda bad.