I have three different species of fish in here, 12 6 inch to 8 inch goldfish, I purchase 10 Rosy Reds which multiplied into roughly 200, also I purchase baby mollies that were about a quarter inch big roughly 10 of them and they've multiplied into roughly 40. I flush my pond with well water once a week for about 2 hours to 4 hours sometimes all night long when I forget to turn it off LOL. I guess I'm doing something right plus she got the nitrates from the fish place and food waste.