A sump is nothing more then a extra tank below the main tank that is plumbed via an overflow. A sump is a place for storage , such as a protein skimmer heater reactors and such. A fuge is a section of a sump that has a deep sand bed, live rock and macro algae to get rid of excess nutrient. The best design I have come up with so far is such. Inlet: where the water enters the sump and goes into a mechanical filtration such as filter sponge or filter sock. Next into your protein skimmer and phosphate reactor. The following section is the fuge consists of a deep sand bed live rock rubble and macro algae, and a algae turf scrubber( you can plumb the return line of the protein skimmer or phosphate reactor to the algae turf scrubber) then the final section is where the water return into the tank.look on YouTube for different sump designs. A good sump would be a 20long 40breeder or a rubber maid container. Rule of thumb is get the biggest sump you can fit under the stand. My stand will not hold a sump so I have mine sitting next to it on the ground. I plan on building a new stand.