What is a Sump?

[IanWR]

When I first started researching saltwater aquariums the thing that I found overwhelming was the concept of a sump. The more I looked into it the more confused I got. The jargon was very unfamiliar and it took me a while to sort it out. So hopefully this description of the 3 broad types of aquarium set up will help explain what a sump is and what it is used for.

Standard Tank

The standard tank is what most people think about as having an aquarium: a glass box. Any equipment that you use is either put directly into the tank (e.g. a heater), or is hung on the back edge (e.g. filter). Having a filter of some sort is used in every tank beyond a goldfish bowl. The filter is used to clean the water. Water gets sucked in, flows through foam, or sponge, or whatever, and returns to the main water. This principle is at work whether you are talking about an internal filter, a hang on back, or a canister.

All in One (AIO)

An all in one (AIO) is like a standard tank that has some portion partitioned off (a.k.a. sump) to be used as a built in filter. There are 3 main advantages of having a sump over a standard tank. First, you are able to hide some equipment from view (heaters, etc). Second, the water in your display tank (a.k.a. DT) will always remain at the same level, as evaporation will only show up inside the sump. Third, and most importantly, you create a situation where the surface layer of water can be filtered. This is particularly important with a saltwater tank as proteins can build up on the surface reducing light and oxygenation. Flow is created through the sump by use of a pump and an overflow. The pump (a.k.a. return pump, or return) pushes water from the sump area through the partition wall into the display.

Water returns to the sump area by spilling over a notch (a.k.a. overflow). Overflows come in a variety of shapes and appearances (some are just a smooth cutout, some are a series of vertical slits, some look like a comb, etc) but they all serve to provide an opening for water to flow over. Every overflow that is not just a smooth notch is only fashioned that way to keep critters from ending up in the sump.

Many AIO sump areas are further divided into sections by walls (a.k.a. baffles). These sections can be used in a variety of ways (mechanical filtration, holding a heater, skimmer, reactor, etc.). One advantage of creating these sections (a.k.a. chambers) is that water in every chamber before the return is at a stable water height, which is very important for certain equipment (e.g. heater, which should always be submerged to the minimum line). Another advantage is that these baffles force the water to flow over and under before it gets to the return chamber. This creates a flow that you can use for filtration (i.e. all the water is forced to go through your filter floss, or carbon, etc). A further advantage to this over and under flow is that it allows bubbles more time to escape and not be sent back into the display.

Sumped System

The sumped system is not radically different than the AIO. All the same principles are the same. But whereas the AIO sections off a part of the tank as the sump area, a sumped system uses a separate tank as the sump. There is still a pump that returns water to the display and an overflow that the surface water flows over and into the sump. The added complication is the many and varied ways to get the water from the display to the sump. For a detailed description, see the article DRAINS 101. The larger sump area is valuable to house much larger pieces of equipment, and gives you the flexibility to incorporate other uses not practical in an AIO sump (e.g. a refugium). The separate sump also increases the total water in your system helping keep your water more stable. For more information on sumps and how they can be utilized, see SUMPS 101.

To summarize, a sump is just a customizable filter that allows for surface skimming and helps keep equipment from being seen in your display. Hope that helps!

[Myka]

Thanks for the great article Ian!