Q. What is a sump?
A. A sump is a tank that usually goes below your main aquarium. It can be made out of glass or acrylic, depending on its intended application. The main reason to use a sump is it provides a separate place to use filtration that would otherwise hang off the back of the tank and detract from the look. There are several advantages to using a sump, the main one being that it makes the main tank look better since it can hold many of the necessary equipment such as a heater, thermometer, protein skimmer, and grounding probe. Another advantage is that it keeps the water level in the main tank constant. Sumps also allow for extra equipment that you could not hook up directly to the main tank, such as; automatic top-offs, in line pumps and skimmers, dosing systems, and monitoring equipment.
While no tank requires a sump, the bigger the tank the more likely hood you will want one. The smallest glass tank that comes with overflows is a 55-gallon, so this is about the size most people start thinking about adding a sump to their setup. The kind of tank you want to keep, be it reef or fish only, can also play into whether or not you should have a sump.

Q. How do sumps work?
A. A sump works by allowing water from the main tank to overflow into it and having a pump return the water back to the main tank. Some tanks are built with internal overflows that allow specific plumbing to quietly drain water down to the sump by means of gravity. Tanks that do not have internal overflows can have external overflows that hang off the back of the tank and use a J tube to siphon water out of the tank and drain it to the sump.

Q. How do I know if I should have an acrylic sump or glass sump?
A. Both glass and acrylic sumps have their advantages and disadvantages. Glass tanks are often much cheaper and easier to come by; however, it is not recommended to drill glass. If you plan on running a RODI top-off directly into the sump or use an external pump you would need to have an acrylic tank. Any external skimmers also require an acrylic sump because it needs to have pluming drilled into the side of the tank to allow water to reach it.
Glass sumps are usually just a box, where as acrylic sumps often contain different compartments, drip trays, and even baffles. These usually help when using different forms of filter media and preventing bubbles from getting into the main tank. Glass sumps usually are 10-gallons on up to 35-gallon tanks. Acrylic tanks are often custom built so you determine the size of the sump. The one down side to have a custom built sump is that it can take anywhere from six to eight weeks to have one built. The Marine Scene does stock a few choices of pre-built acrylic sumps that will work for most size tanks.

Q. Will my sump overflow if the power goes out?
A. Providing the overflows are set up correctly and the sump is an appropriate size it should never overflow. When the power goes off, the return pump stops pumping water and only the water above the overflow siphons down to the sump. Sumps should be set up to be able to hold the extra water for such circumstances.