How to Change Water Filter Systems on a Fish Tank

Written by nicole galipeau
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How to Change Water Filter Systems on a Fish Tank
Changing filter systems must be done carefully to avoid stress to your fish. (fish image by pearlguy from

Changing water filtration systems on a fish tank should be done carefully to avoid killing the important nitrifying bacteria that live in established filtration units. New filter media lacks these beneficial bacteria, which play an important role in the removal of ammonia and nitrite from the water column. Because of this, upgrading or replacing filter equipment requires patience and should never be done overnight.

Skill level:


  1. 1

    Do not turn off or remove the currently operating filter system.

  2. 2

    Set up and install the new water filter system according to the manufacturer's instructions. Rinse any included carbon filters in cool running water, unless the packaging specifically indicates otherwise. This helps to remove carbon dust and other particles that may accumulate in shipping.

  3. 3

    Allow the new filter to run for at least three weeks to a month before removing the older filter system. This helps to ensure that an adequate supply of nitrifying bacteria have had a chance to colonise the new system's biological filtration media, and will prevent your fish tank from undergoing a "mini-cycle," which can harm your fish.

  1. 1

    Set up the new water filter system as soon as possible, and turn it on.

  2. 2

    Remove a portion of the old filter system's biological filter media (usually some sort of sponge, plastic or ceramic ball, or fibrous material).

  3. 3

    Place the old filter media into the new filter system's biological media compartment, alongside the new media.

  4. 4

    Remove the old filter unit, and turn the new filter on.

  5. 5

    Check water parameters daily over the next two weeks to watch for signs of a nitrogen cycle, such as spikes in ammonia or nitrite. If water conditions remain normal over this time frame, it is generally safe to assume that the old filter media did its job thoroughly enough to "seed" the new filter material with bacteria; after one month, you can remove the old filter media and run the new system with just the material it came with.

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