I recently purchased 12 Discus varying from 2.5 - 4 inches and I found the 2.5 were very skittish around the larger fish. I had to eventually spilt them up since the small fish were only getting the left over’s at meal time and fell behind in their growth. If I were to do it all over again, I would have separated them from the beginning. Since the little ones are about a month behind in their development now.