Canister Filters vs. Sumps in Saltwater Aquariums

Written by carrie terry
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Canister Filters vs. Sumps in Saltwater Aquariums
Saltwater aquariums offer a wide array of life. (colourful fish image by FJ Medrano from

Saltwater aquariums offer bright colour, clear water and a wide variety in both plant and animal life. Owning a saltwater tank gives people with limited space and time a chance to own pets and add to the decor of their home. But saltwater aquariums can be tricky, especially when it comes to filtration needs and choices.

Canister Filter

Canister filters are enclosed filters that suck water into the canister, move it through levels of filters, and then push it back into the fish tank. They sit inside a fish tank and become part of that marine aquarium. Unlike some filter systems, they contain both a pump and filter, and offer a choice of chemical, biological or mechanical filtration mediums.

Sump Pump Box

A sump is not actually a filter, but rather an external tank that houses a filter. The sump pump box generally sits below or to the side of a main fish tank, and is slightly smaller. It shares a water source with the main tank through a system of hoses and the filter and pump set-up, so that water is sucked out of the main tank, into the filter in the sump box, and then pushed back into the main tank.

Sump Uses--Refugium

The sumps status as an external tank rather than fixture within the main tank gives it some uses that a standard canister filter does not have. Since the sump is isolated, many people use it as a "refugium." They put young fish that need to grow up and small animals that won't survive the main tank in this side tank for protection. In this case, people generally decorate the refugium with rocks, substrate and plants. The refugium is also useful for growing food sources like krill and algae.

Sump Uses--Storage

Whereas the canister filter is housed inside the main tank, in full view, the sump pump box offers a choice for storage. Many people put the sump box behind the main tank or underneath, in a cupboard, and use it to store filtration equipment and wires or hoses. This keeps the main tank neat and hides away the clutter usually associated with freestanding filters like a canister system.

Sump Uses--Water Capacity

An additional tank like a sump provides another important service by increasing the water capacity of the entire set-up. According to Melev's Reef, increased capacity in a saltwater aquarium "dilutes water of accumulating pollutants, and helps avoid issues that occur quickly in sumpless tanks." This is something that a canister filter can't do, regardless of its filtering capacity.

Combining the Two

A sump may by combined with a canister filter system, since a canister filter also has a pump and therefore fulfils the sump's requirement for pumping and sucking action. Combining these two pieces of equipment is as simple as setting the canister filter up in the sump pump box rather than in the main tank.

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