Sounds like a nice place you got there peeps. As TLF said, 2/3 - 1 HP should do the job. I would recommend placing all the diffusers in the deepest parts of the pond unless your fishery requires otherwise. As far as accessibiltiy to diffuser maintenance goes, you don't necessarily have to pull the diffusers out of the water, that is, assuming the diffuser isn't made of anything organic (i.e. rubber). We service our LDPE diffusers by pouring 1 cup of muriatic or hydrochloric acid down the feeder tubing that leads to each diffuser. This cleans any organic material off the emmitter holes. The amount is relatively nominal and will not affect water quality, harm fish, or damage the diffuser. We do this once per year in our wastewater systems, occasionally in our lake/pond systems and haven't had any problems with diffusers that have been in service for over 30 years. If you decide to go this route, ask your aeration supplier what the diffuser is made of and make sure that muriatic acid will not damage the material. IMHO this is the easiest way to clean a diffuser assuming the diffuser and anything else that will make contact with the acid is made of a material that can handle it. You don't even have to get in the water. Of course, if your diffuser gets covered with inorganic sediments or "plates out" dissolved metals on the emmitters, acid will not take care of it, you will have to access the diffuser. I've never heard anyone mention this cleaning technique on this forum so I hope this is helpful to you and everyone else.
P.S. Muriatic and hydrochloric acid are caustic. Use proper safety equipment including gloves, goggles, and a particle mask when handling.
