Pond cleaning Koi

So my koi pond has about 11 fish in it. Im thinking about completely draining the pond and cleaning it out. TL;DR- New koi pond in new house. Old owner did not take very well care of it. When is the best time of year to drain my pond and give it a good cleaning?

Be careful about doing this. You could end up losing a lot of good bacteria that helps keep the pond clean and clear if you drain and scrub. I made this mistake, eventually I followed a guide here to redo my filter to allow the sludge to get processed. http://www.skippysstuff.com/biofiltr.htm I also built this muck mop. It might be a better option than draining. http://www.waterbugdesign.com/pond/diy_muckmop.html

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