Sarc, Ill give you some hard numbers and some soft ones and you can check with the diffusers supplier for an exact number on gallons of turnover per cfm at your depth. I will assume that your pump is supplying at least 1.5 CFM at the diffuser times 2,plus minimum line loss if a piston pump or a rotary vane.Not knowing your diffusers I will use 1200 gallon per minute turnover if they are not round airstones and you indicate they are not. The math is as follows, 1.5 acre tank 5 ft average brings you to approx 2.5 million gallon/ So you have 1.73 million gallons of turn if you have two diffusers on a single stand or 3.46 million gallon of turn if you have two diffusers each on two stands. Im not sure if when you say 2 diffusers you mean 1 or 2 stands.A 1/4 hp pump (guessing 3-4 cfm) is a lot of air for one diffuser in one spot so hope that is not the case.So 1 stand of two diffusers would give you .692 turns and two sets would be 1.38 turns. Your demand for DO will only increase as your pond matures. I would not want less than "ONE" turn per day to stay in that 70-80 % saturation range, So you are probably not aerating enough with two (stands) diffusers and I would run more.(try 18 hr per day ) And if one stand of two diffussers you are comig up very short. If you want some exact figures see what the cfm output is or tell me the pump brand and diffuser brand and size and I probably have all that info here.When you aerate less when its hot the water will stay somewhat cooler and the DO content will be higher if you can get the cooler water aerated. Since you need to get that cooler water to the pond surface to get it aerated increased temp is the price you pay (not all bad with your fish type) The better news is that you may get some good o2 from your pond being the depth that it is from algae and any rooted plants. Normally the o2 the plants and algae give during the day is consumed at night. The fish are competing with the algae,plants and the decomp process which requires DO 24/7. (thus your pond needing more DO as it ages)86 F water is about 7.5 ppm DO (guessing without your sealevel,salinity etc but real close for this example)70% saturation is only 5.25 PPM DO so not a great number.Lets say you keep the water 10 degrees cooler by not aerating (thats extreme)as much and using the same % saturation you would only gain .66 ppm DO or 5.88 ppm DO.If you were 90% saturated at 86F you would find about 6.8 ppm DO (much better) A level of 7 ppm DO would be great.Try doing a "google search" and type in dissolved oxygen fish and read some of the articles. You are headed the right direction ,The Annis Water Resources Institute has a great one. Let me know if you cant find it,Ted
