Now this is an interesting DIY (Thread form RC)

[BCOrchidGuy]

What about using a small Rio powerhead and use the shaft from a larger Rio, the rios have a hole where the impeller comes.. (I haven't got a clue the technical terms) When you clean your Rio, you take off the outter guard that keeps big crap out of the impeller, then there is the part you turn that holds the shaft in place... That part has a hole, if you used a longer shaft couldn't that work? You'd have to drill the hole out a bit to allow the shaft to turn.....