Hi Tom,

The water falls no more than 1½" in the weir.

This sump doesn't have a bio-tower or wet/dry area, I got rid of all the gubbins and just run simple sponges. It's divided up by baffles into four chambers;
1. Return area. This is where all the foaming is occurring.
2. Poly filter area
3. Course and Fine sponge area
4. Return pump, heating and CO2 equipment

I would just like to know how I can get water to fall 4 foot down a 1¼" pipe into the return chamber without inducing too much foaming as the return pipe seems to be dragging air down with it.
Tomorrow I'll borrow a digi-camera and try and post a shot of the return pipe and sump.