Just getting back to you Ted. BTW, I didn't mean to steal this thread from you Alabama_Woody, I hope you don't mind..
I am using a Gast Rotary Vane pump which is 1/3 HP ( I was going to get the 1/4 HP but it wasn't availible...sorry about the confusion).
Best as I can tell, the diffusers are membrane type diffusers approximately 10.5 inches in diameter. I am using a total of two diffusers at separate locations in the pond. One is at the deepest 'hole' in the pond ~9'. The other is in a deep channel at ~6'-7'.
I would run the aerator the majority of the day during the warm months primarily to boost the DO. My thinking during the cooler months was to cycle it less during the cold days in order to keep some stratification of the pond so that there is warmer water at the surface ( from sunlight). My thinking was this might encourage slightly more feeding with the slightly warmer temps. During these cooler days, I didn't feel that DO was as important since the DO is greater with cooler water. I will however increase the aeration during the days where the ambient temperature is equal or greater than my pond temperature.
I constantly measure and record the temps with a wireless weather station and an additional temperature probe which is located under my floating dock (and always shaded) at 2' water depth.
I do not know for sure if this is the best approach ( I suppose I could invest in a DO meter... but those puppies are quite pricey), but this is at least my thinking. I truely appreciate you input and defer to your greater experince with pond aeration.
Hope this help to clarify things. Looking forward to the continuation of this tread!

PS I have almost a years worth of data so far relating the ambient temp to my ponds temp (at 2' depth). If I can figure a good way to export the data or graphs I will happily do so if anyone is interested.

Sarc