Ponds are just so different, they get dirty fast! I do a full clean out every spring. All fall and winter we get a ton of fallen leaves that rot during the freeze, so by spring it is pretty nasty, where I live, my pond actually freezes over, and my fish hibernate for about 3 months. We don't feed them anything from November until about March, they mostly hibernate, and live on the debris on the bottom. This is the 15th year we have had the pond, and we still have our original fish, so they are pretty hearty! I do a partial clean out every month or so during the late spring to late fall. I will drain about 1/3 of the pond, do a good cleanup of the bottom (neighbor kids love to throw in rocks), and change out with fresh water. Other than that, we clean the main filters every day. It's a lot of work, and most people don't know what they are getting into!