That's a good regimen, but it's really dependent on feeding rates and the accumulation of organics. Best regimen IMHO: 25% every two weeks if you feed a lot or you have a large collection.

Anytime the water starts to develop a haze or a cloudy appearance it's usually a sign of "high organics" and this is a good reason to step up your amount or interval on the water changes. Sometimes, if you're curious about the condition of the water, here's a crude test you can do: Fill a plastic bag with your pond water. Let it sit at room temperature for 36-48 hours with no fish in the sealed bag. Open the bag and take a whiff. If it's fetid smelling, you have problems and a major water change is in order, right away.

Here's an ideal set of regimens:

• Change ten percent of the ponds' water per week OR
• Change 20% every two weeks OR
• Change fifty percent every 6 weeks but no matter what you're doing, you should do a MAJOR 75-80% water change at least twice per year.

People focus on the major water tests we can run and they forget about depletion of trace elements in the water, the removal of excess nitrogen, and the accumulation of phosphates which are a good indicator of overall pond health and background pollution.

Plants in the pond remediate a LOT of forms of background polllution. My aquascape installation has wonderful water quality with no day-to-day or week-to-week maintenence. I have it torn down once a year. Past that it's a piece of cake and has minimal background pollution.

STILL, water changes are a good idea and I am now a staunch advocate of CONTINUOUS water changes at a drip rate. (Look it up!)