Just for additional info... I have one of those "4 cart monsters" on a 36000 gallon pool. I have to clean them about once a month early in the season when tree seeds and cotton wood seeds are abundant but after that I can go 2+ months between cleaning. I alwys clean all 4 and it only takes about an hour. Also I get at least 3 years out of my carts which is good because they add to about 500 to replace.