Before I would consider adding a circulation pump to the sump, I would first consider what I'm trying to accomplish, and how the sump could be designed better or utilized. Detritus is always going to accumulate in a sump, and I've always manually siphoned it out when I'm doing a water change, however, if you're getting an inordinate amount of buildup I would probably think about manual filtration first (i.e. adding an additional filter sock, or running one if you're not); if you see stagnate water on the surface in the sump I would look at the depth of water in the sump in relation to the exit of the skimmer, or carbon/GFO reactor. In my sumps I have the exit down spout on the skimmer maybe a 1/2" below the waters surface......I also return the water from the carbon reactor, not directly down into the sump, but I put a 90 degree connector so the return agitates the waters surface. You can also create flow in a sump by way of baffles, or return pump flow. I would do any one of these things before I put another pump in the sump.
Hope this helps.
Good luck.
