That is a sign of bloat bro. As soon as you notice them acting different, swelling up, white stringy poo, swimming off by themselves means bloat is coming. It may be too late now but start with the eposm food soak. Good luck. The best thing to do with these guys are to put them in a tank that they can grow to reach 4-5" without having to move them so you can reduce the amount of stress.