Hi. I don't have any experience with crowntails, but those who do are likely to ask you a couple more questions. I'll go that part! Size of tank, temperature, filtration, what kind of tank maintenance do you usually do, and if you use a water test kit, what type and what were your last reading (actual numbers are helpful if you know them). That's so that they can get a better overall picture of possible causes and the best treatments.
Lots of people here do have crowntails and I'm sure they'll be able to tell you what if anything you need to do!
Kumi
Lots of people here do have crowntails and I'm sure they'll be able to tell you what if anything you need to do!
Kumi