This is definitely a learning curve project. You will not find a lot of experienced experts for your specific project. My opinion is for your size of 'pond' it is better to use the larger compressor to circulate more water for a shorter period each day. The diffusers in the deepest water will move more water volume per diffuser due to height of the rising water column compared to a similar sized diffuser in shallower water.

It does not surprise me that the windmills are struggling to maintain open water which helps a lot to explain why your trout have been dying each winter.

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