Purchased an old home with and old brick koi pond new back of property. I am located on the Middle Peninsula of Virginia. Pond is an oval shape approx. 5ft x9ft and 3-4 foot deep. approx. 500gal? Pond has large Koi in it but lots of debris on bottom. Water is green to the point that I cant see fish, and have recently found 2 dead Koi. I know several are still alive when they come to feed. No power run to pond currently so ran an extension cord to existing pump. Pump died, and filter was very dirty( canister type) Looking for suggestions on pumps/power source/filtration. Should I just attempt to drain the pond and clean it? Any and all advice appreciated. I can post pictures tomorrow. thank you