Q. I have a 1200-gallon pond that I built two years ago. I have never drained it for cleaning. I just remove leaves and junk as they accumulate. A friend told me that the pond should be drained and cleaned each year to prevent parasites from infesting my fish. How often should a pond be cleaned?
A. I think your friend may have gotten his tip from aquaculture practices. Intensive fish farming imposes management practices that are not necessary in ornamental pondkeeping.
Fish farms — including ornamental fish breeding facilities — may drain ponds on an annual or biannual schedule and either treat them or allow them to remain dry for a year as a method for controlling fish pathogens. This is a necessity for these operations, given the very high quantities of fish that move through breeding ponds and the high densities maintained. But the practice would not have much practical effect in hobbyist ponds, with one exception.
The exception is severe and persistent infestations of anchorworms or fish lice. This would justify draining and cleaning the pond.
If you carry out regular partial water changes and do basic debris and leaf removal, there is little to be gained by draining and cleaning. You will not change pathogenic bacteria or other fish parasite populations substantially, but you might inadvertently stimulate undesirable algae growth (i.e., planktonic algae or long-filament algae) by removing short filament algae on the pond sides. You may also run the risk of damaging the pond or injuring the fish.
Intensive cleaning will also significantly inhibit invertebrate populations in the pond, which will limit its natural quality. All in all, there is little reason to worry about performing this kind of maintenance on a backyard pond.