You guys have good eyes. The big guy has had one girl curled since I got him when he was about 3". I've tried like hell to get it to uncurl, but no success. I think it may be a birth defect rather than a condition from poor water quality. In any case, I don't think there's anything I can do about it.
He eats like a pig and is very active, so I don't think it's slowing him down. I keep the water very clean by overfiltrating and doing water changes all of the time. Feed them mostly raw shrimp. A bigger tank is in the works, but I think I've still got some time.