I agree with tlindsey here. Inbreeding causes allot of problems down the road but there are some things u can do to curb this from happening. 1. You can cull the deformed members of the tank and replace them with new store(s) bought ones. 2. Its a bit cruel but you can let nature run its course and the deformed will eventually die off but there's a major risk of it happening again and again. And 3. Is very similar to 1 but instead of buying new members to replace the culled ones, you cull even more members to try to single out a certain trait(s) or color(s) for line breeding. Granted this means continuous culling over time to get the same trait(s) or color(s) over and over again and again. Or. 4. You could add a small predator to the tank to reduce the reproduction rate. I'm personally line breeding myself. But in order to do so I havto cull juvenile males that don't have the traits I want in the blood line. It's allot of hard work but if your friend is only keeping them as pets I would recommend option 1 as it should have the best results out of the 4