I thought this was kinda funny. Wally took just a couple bites out of his tail a few weeks ago and also started getting red streaks due to the cycling process. So I put him in his own kritter keeper. His tail didn't get any worse, bite-wise, so I figured it was a combination of ammonia/stress of seeing other boys through the dividers. So I put some Christmas cactus around his tank because I thought he might like to feel like he had more plants. Well.... one day I got home and ---boom!!!--- tail GONE! And over the next few days, more and more was gone.
Well, then I realized that the biting coincided with the cactus blooming!! I have since moved it and today his tail is still shredded but it is smoothing out. What a silly boy!