i recently bought two 2'' ntt's. one is thriving and eating alot and the other was always hiding and i didnt see him eat too much. today i found him dead...the other is stable whenever he comes out of hiding and constantly eats. ive read ntt's tend to die like this but my question is should i do a water change or take some kind of action? all the other fish are healthy as can be. ph is 7, ammonia and nitrate test fine