two hours, but if possible once an hour is preferred. A larger pump maybe needed to deliver the necessary flow recommended for the filter and discharge to the waterfall. Measure... the total length of tubing needed. For every 10 feet of tubing add 1 foot of lift to the height of the waterfall from the ponds water surface. Your pump selection will be based upon... the total gallons per hour (GPH) at that calculated the height. The pump needs to pull from the opposite end of the ponds waterfall or the filter discharge. This set-up...