Another consideration may be to extend the diffuser up to the 4 ft area with a simple riser. If for example you have a diffuser that lifts 2300 gpm at 1 cfm at a 9 ft depth simply raising it to 4 ft below the surface would slow it down to 1400 gpm. I would keep it in the same location just raise it and as Cecil states run it at night only. Keep in mind even at 68F at 80% saturation (sea level) you can still maintain 7.27 ppm DO.Pull the overflow water off of the top and continue adding well water. Some DO will diffuse into the bottom water and should give you a desired temp and DO haven to get through the tough summer months.In this case some stratification is desired.Depending on the type of pump and cfm output it may be necessary to vent off some of the excessive air output in the summer months also.Some 1/3 hp pumps supply from 1.5 to 4.4 cfm open flow.This is a situation that you should know the exact specs on your compressor and more importantly the diffuser.