how long would you estimate the 200 watt EcoPlus-7 would take to turnover an .8 acre pond with average depth to 5 feet...is this feasible with tghe pump producing 3660 gph?

Turnover time will be dependent on compressor cfm and size & type & and depth of diffuser and acre feet of water (gallons). A 3/4 ac pond depending on shape might best need two or three diffusers.

compressor is rated at 6 cfm (I believe), its an EcoPlus 7, with two 9 inch diffusers...pond is oblong in shape with avg depth 5 feet....goes from 2 to 10 feet...diffusers are at 9 feet

dracor, I think the ecoplus is lying about the CFM ratings...I just can't see an air pump producing the volume claimed at such low energy usage and with such a small outlet on the pump. It is a diaphragm pump, and will have a LARGE air flow volume drop at 4.5psi of pressure (a 9 foot depth)...I could not find any flow specs from the manufacturer, only specs for the pump weight and shipping volume. Adding much tubing length in the 3/8" pump outlet diameter will rapidly increase back pressure and further reduce the CFM capacity

The Ecoplus7 has been meter tested and shown to loose an increasingly significant amount of cfm as the diffuser increases depth beyond 3ft. Ted Lea tested this at a Pond Boss gathering in Indiana. At 9ft you will be lucky to get 1 to maybe 2 cfm. To casually test this move diffuser/s into 2-3ft of water and notice how much bigger and more bubbles the boil has. The pump is cheap and this is why. It is designed for basically shallow water use.

Depth at 9-10 ft also causes a higher back pressure causing a quicker failure of the diaphragm - more frequent diaphragm replacement.

Pond Oblong shape? length? width? Makes a big difference on complete mixing and turnover time. The water volume of the pond needs to be calculated to estimate turnover.

What type of 9" diffuser - brand name and membrane disk or ceramic stone? Are diffusers together or separated by what distance?

Here is a good OLD read that discusses the EcoPlus 7 that you may find helpful.

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=245867&page=2

I considered the Ecoplus for my 1/4 acre pond, but had the extra cash to overdo it with a Gast pump. And, I think that RC51 has upgraded from the Eco7 to improve his pond's aeration although I think it worked for him for several years.

Keep in mind the link is to a pretty old thread and opinions change over the years. I suspect that you could do "OK" with the proper setup and the Eco7, but without getting all the info gathered up that the other members have suggested (and then some)...it's impossible to guesstimate. The proper set-up would require 2 or 3 diffusers strategically placed out over deeper waters, but only a few feet below the surface (3 to 5 feet), and larger 1/2 or 5/8" line with the runs as short as possible. This systwm would likely need to be run 24 hours a day to meet the bare minimum.

My gut tells me that you would be running a very fine line and if your budget would allow...spend more on a larger system with some extra capacity or add another Eco7 (or two).

NOTE: Pump specs that say "rated at" usually mean that the pump will operate at that CFM...WITHOUT ANYTHING HOOKED UP TO IT. Once you add line, valves, elbows, diffusers, and water depths...diaphram pumps lose output pretty fast.