My name is XXXXX XXXXX I am a Vet tech and have been keeping fish for 40+ years.
Can you tell me have you checked the water Parameters? Ammonia?, Nitrites?, Nitrates? and PH?
Does crush show any other issues?
Any problems with swimming, breathing, or buoyancy?
What size is the tank?
Do you have filtration?
I have not checked any parameters except for temperature which has been on the lower end of the acceptable range for the past 3 or so weeks (since I moved back into a college dorm room--I have tried to turn the room temp up, but it is really out of my control).
As far as I can tell he doesn't have any other issues that I have noticed except for when he is trying to turn it takes him longer than it used to in order to face in the direction he is trying to go. However, once he is the right direction he has no problem moving forward or back.
The tank is a small square 2L tank with no filtration
When we see problems like you described it can be a result of the water quality. Ammonia spikes and Nitites can cause problems. What I suggest since you stripped out the tank and cleaned it is to get some Fritzyme #7 or Bio Spira, which are nitrifying bacteria. When you clean a tank and the gravel you actually will start the tank go through a new cycle, which means you can face New Tank Syndrome: http://www.bestfish.com/breakin.html If we use the Nitrifying bacteria like what I have suggested this will help the tank cycle faster and stop some of the problems you will face. The mid 70's -82*F. We want the Ammonia at 0, the Nitrites at 0 and the Nitrates at 20ppm or less. The PH at 7.0. If the water parameters rise we need to do some partial water changes to help get them back to normal. If the water parameters are normal the tail issue should straighten out, unless it is a genetic defect from inbreeding. When you feed do it in small amounts, so there is not a lot of residue left in the tank, this will also help keep the water parameters from being incorrect. Shredding of the tail is usually a result of the ammonia being high, so I think if you can test the water on a regular basis and make sure to get through the cycling time which is usually 30 days, Crush should do well. Please let me know if you have any questions and I will be happy to continue with you. Joan