grosse gurke said:There really is no formula, too many variables. Different fish grow at different rates achieving different sizes. It also depends on if you are looking too keep fish in that size for life or a few years. I use the theory that if they looked cramped, they are. Therefore, I had 9 pygos in a 125 ranging from 5" - 8", looked and felt cramped, so now I have 8. When that starts to look and feel cramped, I will have 7.
There is no science to it; I just go with my gut.