Water Daphnia eat green water, but fish eat Water Daphnia. UV sterilization works but you have to have the right size and flow rate for your pond, larger ponds are too expensive. I use the plant "water hyacinth" to keep my koi ponds clear. Water daphnia live in the roots and fish will tear the roots out trying to get to the daphnia so its best if the water hyacinths are in a pond away from fish especially koi. Water hyacinth are a heavy feeder and utilize ammonia directly and work best with flowing water going through their roots. I keep a 20,000 gallon pond stocked with 800+ pounds of koi clear all summer in full sun with a 8,000 gallon flow rate through a 200 square foot area full of water hyacinths.

These ponds also have filtration systems that pull sludge off the bottom, and are aerated heavily which is also key. Fish produce Ammonia, which gets turned into Nitrates by bacteria. You have to remove the ammonia or the eventual Nitrates otherwise you are going to get green water. Nitrates can be deluted with water changes, or expelled as a gas using trickle towers.

Last edited by Bickal Koi Farm; 12/05/12 10:21 AM.