Our corporation is running 8 diffusers off of six pumps. Four of the pumps are 1/3 hp and just run one diffuser each. The two other pumps are 1/2 hp 220 volt. They run two diffusers each. All are vane type pumps. The diffusers are in water 10-20 ft. deep. What we have been told is not to put any diffuser in water less than 10 ft. deep with the best results in the deeper water. Over the years we have expermented with different diffusers and have setteled on the membrane type because they are easer to maintain and also to kick up in the early spring. They seem to clean themselves. A rule of thumb that we go by is to kick them up when the water gets 60 degrees and turn them off at the end of October. We may kick one up in the shallow end in the winter time to keep the lake open if ice forms. Then turn them off when it clears. If you have one going in the deep end in the winter it circulates the water to much and keeps the lake colder for the fish.