I have briefly looked at a working sump system at a friends shop and think it looks like a good idea but I have a few questions. First would be what kind of pumps are you using and where are you getting them? Does the water that is being filtered only come from the top of the tank? If so wouldnt it be better if you were also filtering water from the bottom of the tank to collect particles that are settling in the tank? Im not entirely sure of the whole design principles.