hello,does anybody totally pump out there koi pond once a year? I have a 20000 gal pond and wanted to know if and when its a good idea to pump it all out. I am assuming the best time to do so would be when the pond water temp is the same temp as the water coming out of the garden hose? I have never had a reason to do it in the 6 or 7 years I have had it. I have never had any build up of any kind in the bottom except in the spring time from the fall leaves. the kids get all that out when they start swimming in it. any advise?