Greetings everyone,

I've got a ~2,500 gallon pond, very basic. Pretty shallow, max 2' deep, no filter, one pump at the bottom piped to outside the pond when I want to clean the pond (about twice a year, late fall after leaves are gone, and early spring), and one incoming from freshwater filling from a cistern fed by a well. Both fairly high flow, 50gal/minute. Had it for several years, been great, built more as a water hole for wildlife than anything for fish ... I use back/blue colorant and algae has been in check ...

Three years ago I stopped by petsmart and could not resist ... Got five goldfish at 25c each ... Didn't feed them, (someone told me it was unnecessary) and they grew to 2-3" in the summer. Come winter I installed a 200w floating heater. I am in Colorado, and I typically get the entire pond frozen solid, about 3-4"ice. Following spring, there were my goldfish, seemingly as happy as can be.

The next winter was a different story. I did the same thing, (floating heater), but in the spring, all I found were whitish dead bodies ... Yet that winter was not particularly colder ... Not cool, not cool at all ... Last year, same thing (with new ones).

What is it that killed them? Stagnant water/lack of oxygen? Water too cold? Food?

Last spring, I could not resist again and got 5 goldfish and two koi, and I am determined to do better. I've read koi typically need deep water (4' +?) so I am quite worried. Any recommendations for improvements? Would circulating water help? More heat? Air? I''ve also considered transferring them to my cistern (400 gallon concrete, 3' diameter) for the winter, it is buried with only a small opening on top and never freezes , but wouln't light and food be an issue? Although I could add lighting I suppose ...

Any thoughts?


Thanks much,
JDS