There is a small water pump CPR is now recommending for their overflows. They are called Aqualifter. It has two spots for airline tubing. One line sucks water and air into the pump and the other spits the air and water back out. (You hook up the line that sucks out the air and water to the nozzle on top of your overflow). This little pump will sit right on top of your overflow.
Works perfectly. The powerhead never worked worth a crap.