My crowntails were my prettiest bettas and they were such a rare find for where I live, and they've both got fin rot! I'm treating it, but their crowny spikes have already rotted off very quickly. Sucks so bad.
Sorry to learn about the finrot. It's one of those things that are hard to avoid if you keep fish in small uncycled tanks.
What are you treating it with? Even though you are giving it a course of treatment, be sure to keep up with the water changes. That's so very important to healing and preventing finrot.
I've been treating with maracyn by mardel. I do regular water changes, 50% every wednesday and 100% on sundays. So 150% every week.... that is enough isn't it? I'm on day 3 of the treatment, I'm hoping the fin rot has stopped, but it was a pretty nasty case.....
I hope your fish is recovering nicely by now. Just in case the Maracyn does not clear it up, you might want to be aware that your fish could have a secondary bacterial infection, too.
If it is a bacterial infection, the culprit is usually Columnaris. The secondary infection that you will want to be on the lookout for is caused by a bacteria called Aeromonas. It may be treated with Maracyn 2.