I feel so bad that this has happened though. We had only just gotten his dorsal out to where it seemed like it was going to stay and now this happens to him. That the fin rot is back (as I assume this is what happened to him before we bought him) is rather disappointing as well.
He seems to be acting ok still. He has started a kill-the-bubble game but blowing a tiny bubble and then attacking it... Along with snapping at his filter from time to time. I think he's upset at the fact it stopped working for a minute because it wasn't sitting right.
I was sitting here watching him and then got the o_O going because he started biting at the filter. As you know, that is not like him at all. He loves that silly thing and uses it as a fishy-treadmill. So his biting at it and jumping and biting at it was very odd. Then he started to flare and attack it. So I checked on it. Turns out, it wasn't sitting properly so it wasn't pushing out water. So dear Hannibal was upset about it. Now that it is working properly, he's still going over about once every 3 mins or so to give it a little bite.
Mostly he is now playing kill-the-bubble. This is only interrupted long enough to give the filter a bite now and then and then when I gave him some dinner. He gobbled it up like he's been starving. I think frozen foods are in his near future to give him extra protein for growing back the dorsal. Again. That is... if he'll eat them. -_-
Update: Despite all my efforts, his dorsal is now one thin ribbon with that being at the back nearest his tail. More of his tail is also gone. I'm not sure why it keeps advancing like this, but if it continues he'll end up with no fins. He was such a pretty combtail until yesterday!
His behavior is still normal for him. He's still very active.
I dunno, Enkil. This really sounds like finbiting or he got caught in his filter. If he had such severe rot that his fins were falling off like that, he would also be acting very sick. He would be lethargic and not eating. I'd start by baffling the filter (hopefully he won't hate me for suggesting that) and making sure all suction cups are attached. Try switching his decor around a bit. You can still look for the Kanaplex to have on hand but HOLD OFF on treatment for now.
I double checked all suction cups today to make sure that I did get them on properly last night. They were all fine.
If he's managing to take off his dorsal this badly with biting and possibly thrashing, I hate to say it but... I'm impressed.
His activity level is holding pretty steady. His appetite is good. Got very upset with me for being late with his evening meal but I had been cooking. His meal was 5 mins late at the most.