Tail biting. Just keep the water as clean as possible and carefully re-evaluate different aspects his environment for possible sources of stress, i.e. water quality, temperature fluctuations, water parameter fluctuations, proximity to other bettas, proximity to reflection, lack of hiding places, strong current, etc. If you get to the root of the problem, he should stop tail biting. It may not be a trigger you expect, though. One of my biters didn't like being in total darkness at night, so once I got a dim night light he stopped. Another one didn't like a certain piece of decor in his tank--once I removed it, he stopped biting. You just have to go through a process of elimination until you figure out his trigger.
Last edited by Adastra; 09-30-2010 at 12:34 AM.