[Regenmeneer]

Quote: I do not believe there should ever be a need for a "spring cleaning" in a properly designed pond, because the bottom drains should have picked up any appreciable amount of debris/sediment. But, I realize we all have to deal with what we have, which is often not as well-designed as we would like.

I have to agree with Mike, but we've all ahd our share of imperfections in a pond somewhere along the road. So when you have the chance, try to fix the problem or build a better pond. Untill then, IMHO, you should clean your pond in fall, before temeparatures really go down. This way the bad bacteria are deprived of places to thrive and bug your koi when they are most vulnerable.