This is our 2nd pond. We have about 24 koi, 4-5 years old. They all grew at least 4 inches this summer. I fed them 5-6 times a day. We are re-doing our other pond. That is also about 2000 gallons. This pond has a bio-filter and 2 fifty gallon drum filters. It seems to do the trick. The water stays pretty clear.