I don't think I have any koi left in it right now. I think a heron got them. That and my bio filter never kicked in before winter. I drained two thirds of the pond water two weeks ago (the water looked like pea soup) and I saw no signs of fish life. When I started my pond project I was told by an employee at the garden store that managing a pond is just like keeping an aquarium just out side. HA!! she should be horse whipped. I'm finding out that she was wrong. I found a wonderful ma and pop nursery which actually specializes in raising goldfish and koi about ten minutes past the bad nursery where i first went. I guess most of the problems in my pond was in the flow rate of my water through my filter box. to fast; bacteria never had a chance to colonize. So I slowed down my flow rate, diverted the water flow from the pump directly back to the pond, by passing the filter so of that 7500 gallons an hour being moved through my pump only about 700 gallon per hour flows through pea gravel and carbon in my filter box.