I like to clean mine before winter but if needed it can be cleaned in the ASpring to. If I get a huge build up of crude, I'll use my vacuum during the Summer too. I run 2 4800 gal/hr pumps with large Oasis filters which need the filters rinsed daily and the grills of the pumps removed and cleaned once a month. I also run a large air pump to aerate the pond during the Summer when the water is less able to hold as much oxygen as in the winter. Best to go by the quality of water by using a test kit to be sure Ammonia, Nitrates and Nitrites are kept in check, DON'T let the look of the water fool you. A crystal clear pond can be a death trap and you don't know it untill you test that water.