Overflow Power Filters for Aquarium (Setup and Maintenance Guide)

The filter box for overflow filters is located outside the tank. An impellor-driven pump draws water into the filter box via an intake tube and returns it to the aquarium in a larger stream, commonly aimed over the water surface. Most overflow filters have changeable cartridges and, in many cases, space in the filter box for extra filter material. Replaceable cartridges are typically intended for mechanical and biological filtration, with some including carbon.

Some overflow filters additionally have a biological filtering system. With the addition of proper media, any overflow filter with enough room in the filter box may be converted into a very effective biological filter. A suitable biological filter medium will have a broad surface area (without impeding water flow) and should not need replacement.

Extra filter media may be added to an overflow filter when there is room to offer further mechanical or chemical filtering. The sponge may be used to offer additional mechanical filtration as well as some biological filtration. Where chemical filtration is needed, carbon, zeolite, or resins may be added.

Overflow filters are often used in small to medium-sized tanks. Smaller variants may lack the room for additional filtering material and work similarly to an internal power filter. Overflow filters, on the other hand, offer certain benefits over internal filters. For starters, the majority of the filter is located outside the tank, which is more visually pleasing and allows for more area in the tank for fish and decorations. They may be used in extremely tiny tanks to offer filtration without taking up too much room or producing excessive water turbulence. They are ideal for seahorses and planted tanks because the slow flow of water offers effective filtration without introducing too much current. They’re also great for tropical community fish and tiny to medium-sized coldwater fish. They may struggle to keep the water clean in extremely lengthy tanks or if huge dirty fish are housed.

The relatively expensive cost of replacement filter cartridges, which must be replaced every few months, is a downside of certain versions. Some variants enable the use of a sponge or poly pad instead of replacing cartridges, which lowers recurring expenditures. Others employ longer-lasting sponge pads, which saves money while improving biological filtration.

Getting the most out of this filter system:

Choose a model that is appropriate for the size of your tank and the quantity of fish (Remember that good filtration requires turning your tank volume over three times an hour, more filtration may be needed if you have more or larger fish). Consider the available space for additional filter media as well as the cost of new cartridges and their estimated lifetime if money is a problem. Use additional filter media if feasible to meet the demands of your aquarium.

Regularly clean the filter cartridges (or equivalents). If you depend on them for biological filtration, gently rinse them in aquarium water. If you use additional biological filter media, the cartridges may be cleaned with cold tap water, but do not scrape them or they will wear out faster. As required, replace the cartridges (or replacement) and any chemical filter medium. If organic debris accumulates in your biological filter medium, gently rinse it in aquarium water rather than discard it. Replacement cartridges may be seeded with nitrifying bacteria if necessary by putting them in the aquarium or filter box for a few weeks before they are required, or by washing them in the aquarium water with the old cartridges. If your overflow filter has two or more cartridges, you may change them individually rather than all at once.

Clean the area surrounding the impellor every 2-3 months to guarantee smooth operation, and replace the impellor if required.


Problem: The filter does not run, i.e. the impellor does not spin.

Possible causes and treatments:

  1. Examine the power supply, ensuring that the filter is connected in and switched on at the power source.
  2. The impellor may be jammed: mild shaking may restart the filter, but the impellor or impellor well may need cleaning.
  3. Faulty/worn impellor or broken shaft: inspect the impellor and shaft and repair as necessary.
  4. A burned-out motor or faulty wiring cannot be restored; instead, the filter must be replaced.

Problem: The impeller rotates, yet there is little or no water flow.

Possible causes and treatments:

  1. Filter media that is clogged may be impeding water flow: rinse media in aquarium water and replace as required.
  2. Water intake strainer or tube restriction: clear any dirt from the strainer, rinse out the tube or clean it with a flexible brush.
  3. Air blockages in the intake: add extra water to the rear of the filter and shake the intake tube.
  4. Faulty/worn impellor: Check the impellor, make sure the fan is securely attached to the impellor (some spin and click, but only about a quarter turn free play), and replace the impellor if necessary.

Problem: The filter generates excessive noise.

Possible causes and treatments:

  1. Air in the intake tube: This is typical when the filter is restarted, but if the noise persists, try jiggling the intake tube, stopping and resuming, or putting extra water into the filter’s rear end.
  2. Faulty/worn impellor or shaft: inspect the impellor and shaft for wear and replace them as necessary.
  3. Loose intake tube: double-check that the intake tube is securely placed.
  4. Running water noise generated by water dropping back into the tank: increases the water level in the aquarium.

The filter is working well, however, the aquarium is not staying clean.

Possible causes and treatments:

  1. Clogged or old media: Rinse the cartridge(s) in aquarium water and replace if necessary.
  2. Fresh new media that has not been seeded with bacteria, and media that has been cleansed of beneficial bacteria: When the filter is brand new, good bacteria will not be present, and the filter will not function properly. Good bacteria aid in the breakdown of waste and the trapping of small particles. If you clean the media with chlorinated tap water or detergents, or if the media is left to dry up or is deprived of oxygen, the beneficial bacteria will die and the filter performance will suffer. You may add healthy bacteria cultures to help them establish (or re-establish) in the filter.
  3. Inadequate filtering for tank load. Even if the filter is working effectively, filtration may be insufficient if it is not a suitable model for the tank size, or if the tank is overcrowded or filled with highly filthy species. Increase the frequency of maintenance, lower tank load, or enhance filtration.

Water seeps from around the motor.

Possible causes and treatments:

  1. Worn or inadequately sealed O-rings: inspect the o-ring condition, lubricate or replace if worn
  2. Cracked filter body or connections: Replace the faulty parts (if available) A new filter will be required otherwise.

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