Sizing is simple in most cases. The Aerators Horsepower is equal to the surface acre you need to aerate. For Example: 1/2 HP = 1/2 Acre Ponds and so on. These High Volume Surfaces Aerators Range from 1/2 HP - 5 HP. 2 HP -5HP have 3 Phase Aerators as well. In waste water applications it may call for more Aerators to accomplish specific goals before Discharging water into city sewer systems or into other water ways. Contact us or complete our Pond Survey for assistance.