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How to Change Aquarium Filter without Losing Bacteria

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by Jason Matthews


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Since you are keeping fish, you already may know the importance of ensuring the presence of bacteria in your aquarium. These beneficial bacteria prevent the spike of ammonia, nitrates, and nitrites in the water – these can be harmful to the fish and other marine life that you keep in your aquarium.

If it is nearly time to change the aquarium filter, you may worry about how to do that without losing the beneficial bacteria. Often, inexperienced aquarists end up losing bacteria when they change their aquarium’s filter. Also, when you install a new filter, it can take a few weeks to build up the presence of beneficial bacteria. While this can give you some solace, remember that even a few days without beneficial bacteria can be detrimental to the health and wellbeing of the fish.

Related article: How often should you change filter in your aquarium?

So, here are some tips that will teach you how to change the aquarium filter without losing bacteria:

Retain the Old Filter after Installing a New One

The easiest way to ensure that your aquarium does not lose bacteria is to retain the older along with the new one for at least a month. When you do this, the bacteria will colonize the new filter.  After a month, you can get rid of the old one without worry.

Just remember to keep a watchful eye on the flow rate of both filters. If it is too strong, it will stress out the fish, especially if you have bettas and small and young fish in the tank. The fish will have to swim against a current and that will tire and stress them out. Also, if you are growing live plants in the aquarium, you do not have to worry about the carbon dioxide level. The slow flow of water will maintain optimal CO2 levels.

See also: How long time does carbon work in your aquarium filter?

Install a New Filter but Reuse the Media from the Old Filter

A green beautiful planted tropical freshwater aquarium with fishes

Another way to ensure that you do not lose the beneficial bacteria when you change the aquarium filter is to reuse the media from the old filter in the new one. The media is filled with bacteria and if you reuse it in the new filter, you do not have to worry about losing the bacteria.

You do not have to reuse the entire media. Just use half of it so that the new media that you use with the new filter will have sufficient time to get colonized and it will not cause an imbalance in the aquarium water chemistry. Alternatively, you can use just the old media without clubbing a part of it with the new media. Just make sure that the old media is in good condition and it fits into the new filter with ease. Retain the old media for a month before you replace it.

Use Two Filters in Your Aquarium

Another option to ensure you do not lose bacteria at the time of changing the aquarium filter is to use two filters in the fish tank. That way, you can install a new filter and media without worrying about the loss of the bacteria. The other filter will have a sufficient colony of bacteria to also colonize the new filter.

Of course, make sure that one filter is smaller than the other and adjust the flow rate of the filters so that it is not too strong for the inhabitants in the aquarium. This method is better suited for medium-sized and large aquaria.

The Bottom Line

Use one of these methods to change the aquarium filter without losing bacteria. You will find that these methods are simple yet effective.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

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