Sorry I haven't been a part of this thread since it began, but was away out of country for a while. I also have that model of pump and run it 2 to 4 hours at a time with about 6 hours in between running to cool down. I have never even had the pump warm to the touch. It pumps nicely through the aerator that I have on it and it does not seem to have a problem. I also have the manual and it does not mention a fan and it won't because it can be used for many applications not just what we are using it for.
I have used these and other similar pumps in my industrial applications and don't seem to get the high temperatures that you are seeing. Either the system/stones are not matches and the pump is drawing more current to pump the same amount of air or you have a pump that is not in good shape. Either way I would check into seeing the root cause as opposed to slapping a fan on the system without knowing why it is overheating.
I hope all goes well and runs quiet and cool !!
