What is an Aquarium Sump Tank?

Posted on July 03 2024, By: Aquarium Dimensions

Sumps: A Separate Home for Accessories and Essentials

An aquarium sump is a separate tank that is plumbed into your main tank from below. It contains essentials like filters, heaters, and protein skimmers. Offsetting these items provides easier access to them and saves space around the main display tank (where the fish live). They are most often implemented in saltwater aquariums, but they're used for freshwater also.

Aquarium Sump Tank Placement

A sump is usually placed inside the cabinet of an aquarium stand. Sometimes they are placed in a separate basement or a fish room on a larger build, which offers more accessibility. Regardless, return pumps push water back into the main display tank from the sump.

Sump Tank Benefits

Sumps offer extra space to conceal your equipment, give you more flexibility for accommodating a great filtration system, and house a secure place for plants in freshwater aquariums or macroalgae and fauna in saltwater aquariums.

Step by Step: How an Aquarium Sump Tank Works

1.    The water flows from the display tank to the aquarium sump, usually passing through a filter sock that removes debris or any large particles.

2.    A protein skimmer removes organics using foam fractionation.

3.    Water is biologically purified when it enters the refugium area.

4.    The microbubbles are trapped when the water passes through baffles.

5.    The return pump forces the water back into the display tank.

Components of an Aquarium Sump Tank

Filter Sock                                                         

A filter sock is usually used as the first step of filtration to remove any particles present in the water. As the water flows from the display tank into the filter sock, suspended particles get trapped in it and eliminated from the water. The socks must be replaced when they get dirty and clogged up. 

Protein Skimmer

After passing through the filter sock, water enters into the protein skimmer, where organics are removed using foam fractionation. The protein skimmer can be installed anywhere in your sump, but it is best to position it upstream the refugium. If placed downstream, the skimmer can suck up beneficial invertebrates produced by the refugium. 


The refugium is that part of the sump that removes impurities from the water naturally. This is done by the organisms living in the sump refugium area. Many fish hobbyists keep a deep sand bed in the aquarium sump refugium. This deep sand bed provides a growing area for beneficial bacteria and invertebrates. A typical sump refugium may also contain Chaetomorpha or other macroalgae that remove nitrates, silicates, phosphates, and other impurities naturally.


Generally, after the sump refugium, water flows through a series of baffles. Baffles are trap bubbles by forcing water over and under narrow walls. 

Return pump                              

The water is then sent back into the fish tank via a return pump. 

Other Components

The preceding is only a basic set up for a sump. Some hobbyists add other components, too, such as heaters. Getting the sequence correct is most important regardless.


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