A sump-pump aquarium sits outside the main aquarium and houses your pump and filter. This setup increases the tank's water capacity, which is especially advantageous for saltwater environments because saltwater is easier to maintain in larger tanks. A sump pump aquarium gives you a way to hide unsightly equipment, keeping the main tank tidy. Setting up a sump-pump aquarium in your home is easy.
Take your fish and other animals out of your main tank and put them in a holding tank with some of the water, to sit until you're ready for them again. Drain your main tank using a hose into the sink, so that you're working in a safe, dry environment. Set up your design ahead of time, while both tanks are empty and easy to move. A sump pump aquarium can be smaller than the main tank, but should be big enough to house the pump and filter comfortably. Put it behind your main tank on the stand, if there's room, or under the main tank in a cabinet or beneath the stand you're using for your setup.
Drill two holes, slightly larger in diameter than your plastic tubes (available at fish supply shops), using the power drill. Drill the holes in the back or side of the tank, depending on where your secondary aquarium is going to sit. It's best to drill holes in a wooden side, if your aquarium has one. Push the end of one hose into the first hole, and repeat with the second. Paint a waterproof sealant around the outside of the hole to seal the hose in.
Place the pump and filter anywhere in the sump pump aquarium and attach the free ends of the hoses to the pump. Each hose should be able to reach the pump without kinking or stretching. Attach one hose to the "out" function of the pump and one hose to the "in" function, so that the pump works to both suck water from and return water to the main tank (these functions should be labeled on your pump). Attach the filter to the pump as usual.
Fill both tanks with treated water and turn on your pump and filter setup by plugging it in or turning on the power switch. Monitor the water flow for at least an hour to watch for leaks and overflowing before you put your fish back into the main tank.