Instead of using a fan to cool the pumps I would use a 12v PC extraction fan to vent the heat back in to the room...this will help heat the pond and the air in the room. You have paid for that heat in your electricity bill.....you may as well make use of it.
I think you can run those fans off cheap Solar panels....you could even run the solar panels off the tank lighting for more free / paid for energy but if you do that you need to add ventilation for when the lights are off.
My swimming pool pump runs pretty hot but it was designed that way.
The pond water also cools the pumps anyway.