Redundant Aquarium Filtration

Using More than One Filter on Your Fish Tank

Though it is true that if you use more than one filter on a tank, it is likely that neither filter will perform as efficiently as it would alone, this is expected because of some of the restrictions placed on filtration systems by water volume. This parallels the rationale behind not using bacteria boosters in a tank once the tank has become established.

Should I Use Redundant Filtration on My Fish Tank?

I almost always recommend using redundant filtration in a tank. The reason I recommend this is that if you have a filter fail for whatever reason, you have a backup in place that is already cycled and nearly capable of handling the load in the tank immediately. This can buy you some time to get to your local pet shop and get the parts you need to fix your filter or to get a replacement filter, without leaving your tank unfiltered while you are doing this.

Why Use Multiple Filters on an Aquarium?

The most common reason I give for not recommending redundant filtration on a tank is if one or more of the alternate filtration methods is not appropriate for that tank or setup.

The capacity of a biological filter, provided that you have sufficient filtration to support enough biological filtration for a tank the size of yours, is determined more by water volume than by the number or configuration of the filters being used.

An Example of Redundant Aquarium Filtration:

If you have a 120 gallon tank, and you have a power filter that is designed to support your 120 gallon tank, and you use only the power filter, you will have enough biological filtration to support your 120 gallon tank.

On the other hand, if you have a canister filter designed for your 120 gallon filter, and you use your canister filter, and you use a good biological media in it so that it can provide biological filtration for your 120 gallon tank, you will also have enough biological filtration to support your 120 gallon tank.

If, on the other hand, you use both of these filters, you will have enough biological filtration to support your 120 gallon tank - not enough to support a 240 gallon tank.

However, if you were to use these same two filters on a 180 gallon tank, you should be able to provide enough biological filtration for that 180.

Are there Drawbacks to Redundant Filtration?

However, as always, there are exceptions to this rule:

• If there is an under gravel filter involved, the filtration may not scale. Under gravel filters that do not effectively cover the entire bottom of the tank and efficiently use the entire substrate as a filter can have the negative side effect of creating anaerobic pockets in the portions of the gravel that they do not circulate water through. These anaerobic pockets can produce toxic gases that could pose a health threat to your fish. So, it is important to remember that if you are using an under gravel filter, the filter should cover as much of the bottom of the tank as possible to provide efficient filtration.
• If the filters in question are minimal to the smaller sized tank (in this case the 120 gallon tank) they will be insufficient to the larger tank, because the shortcomings can be compounded and it is likely that the water will not be sufficiently circulated.

What this example is intended to demonstrate is that adding filtration to the tank, provided that the initial filtration was sufficient to the tank, does not increase the tank holding capacity in any significant way, nor does it use any one of the filter elements to its maximum capacity or efficiency. However, redundant filtration on your fish tank will be highly beneficial in any case where you need to disable one of the filters for a period due to a mechanical failure or due to medication.

My snail mail address is: Keith Seyffarth, 217 W. Koch, #308, Bozeman, MT 59715.
Thank you for your support.
Page most recently modified: February 11 2007 19:19:37.