BC29 Filter
I set my BC29 up two weeks ago an have been having the same problem intermittently. At first I just kept cleaning the white pre-filter which would allow enough water flow to keep the pump chamber full. Well, after a lot of debris and sand being caught and cleaning the filter several times it started to get chewed up. This morning the pump started to run dry again so I went and bought a new pack of filters. I put a new filter in and the pump runs completely dry right away so I am baffled. Cleaning the filter has worked so far so how can a brand new filter make the problem worse?
Well, after cleaning the blue filter, moving all the live rock ruble away from the exit of chamber two, etc. I started moving the filter around in chamber one. Basically what is happening is the filter sits so close to the divider between chamber one and two that it causes suction or reversion, some kind of pressure build up which doesn't allow the water to pass through. Looking from the front of the tank, the filter slides in to two vertical grooves facing perpendicular to the front of the tank. You can slide the filter to the left of the two grooves and you can actually feel it suck up against the divider and stop water flow completely. If you place the filter to the right of the two vertical grooves it leaves a little more space between the filter and divider. The water still flows through the filter and doesn't create all the pressure build up, problem solved. Try it out, it is working for me.