When to Change Fish Tank Filter Cartridge?

Everyone who enjoys maintaining fish in aquariums is aware that good purification is one of the most important factors in aquarium success and enjoyment. 

Anything just under 100 per cent effective filtration will result in cloudy, foul-smelling water that is bad for everyone around the aquarium and the condition of the fish kept within.

Therefore, cartridges need to be replaced more often once they lose the ability to give maximum filtration. I am going to discuss how often and When to change fish tank filter cartridge and how to do it. 

When to Change Fish Tank Filter Cartridge

Does The Filter Cartridge In The Aquarium Really Need To Be Changed?

Frequently changing the aquarium’s cartridge is not even necessary. Although keeping the tank clean and maintained is important, many choose to replace the cartridge within the routine cleaning cycle so that they can do so safely.

This is a bad idea because it will just waste money changing cartridges frequently and eliminate healthy bacteria unnecessarily.

In the absence of a genuine need to replace the filter cartridge, it is unnecessary to risk the loss of helpful bacteria and stress your fish.

When To Change Fish Tank Filter Cartridge?

At least once each month, the cartridge needs to be replaced. or if you observe a discernible drop in water flow.

Every cartridge has a different life expectancy, and each cartridge maker will typically offer fairly unbiased recommendations regarding how long you may extend the cartridge’s life. 

However, a seasoned aquarium enthusiast will have developed a sort of sixth instinct regarding the need to replace the cartridge.

The sound of the filter motor straining against an already clogged filter, the smell and feel of the water within the tank, and the condition of the cartridges themselves are typical indicators of this reality.  

Nothing in the aquarium has a greater potential for harming the fish than dirty water, thus every effort should be made to prevent this catastrophe.

Aquarium filter cartridges typically have a lifespan of four weeks. However, this goal can only be met if weekly maintenance is done on the filters on a regular basis.

Filter cartridges don’t cost a lot, so it’s a good idea to always keep two sets on hand in case one needs to be replaced.

Changing an Aquarium Filter Cartridge in Three Different Ways

When replacing the tank filter cartridge, there are three major strategies to avoid losing microorganisms. These approaches are rather straightforward and call for retaining the used filter cartridge.

So, whether you are replacing the whole filter or only the cartridge, be careful to keep the old one around to assist the new one.

This prevents the potential catastrophe that might otherwise happen in the tank by allowing the new media to gather the germs from the old one. These are three approaches:

1. Retaining the Previous Filter in the Aquarium

The most efficient and convenient way to avoid bacteria loss is to leave the old filter or cartridge in the aquarium alongside the new one for four to six weeks. The old one needs to be removed after about a month and the new one installed.

By using this technique, the aquarium’s balance will be maintained by giving the new filter cartridge enough time to develop the good bacteria from the old medium.

You must, however, pay special attention to the flow rates. The fish, especially the young and little ones, will inevitably be disturbed by the rapid rate of flow.

The fish are more stressed when the flow is rapid because they are continually swimming against the river. In order to maintain a healthy amount of carbon dioxide, a moderate flow rate is essential for both live plants and fish.

If necessary, filter pads could be employed to lower the flow rate. If you like, you can keep the used cartridge there permanently, provided it has not malfunctioned.

2. Getting the New Filter Colonized

There is yet another alternative available if you are unable or unwilling to run two filters at once and the old cartridge does not fit the new filter.

Take out the filter’s cartridge before removing the old one. Simply put it into the tank with the new filter after ensuring it is in excellent condition.

It will function similarly to inserting the old cartridge into the new filter, provided that the media is not disintegrating. The old cartridge’s bacteria would have colonized the new filter within a month.

This technique can be used for a month only, even though it is secure to run two filters concurrently in the aquarium continuously or keep recycling the old cartridge in the new filter till it starts cracking.

If the old cartridge is still in the tank after the month is over, remove it right once because it can start creating issues.

3. Knowing the Importance of Minimizing Bacteria Loss and Biological Filtration

Most novice aquarists aren’t aware of how crucial bacteria are to an aquarium’s ecosystem. 

Many people replace their tank’s filter too quickly and eagerly, removing most of the helpful bacteria without considering the potential effects.  Usually, there are serious repercussions from this.

The necessity of preventing bacteria loss during changing filters, or even just the filter cartridge, must be understood by all aquarium owners.

The process of biological filtration uses bacteria to help purify aquarium water and maintain the aquarium’s health.

The major waste disposal mechanism in the tank is run by the helpful bacteria that gradually accumulate on the filter and the cartridge.

Ammonia is released into the aquarium water by all of the leftover food and your fish’s waste. Fish health can decline and even become lethal if there is a substantial number of this ammonia present.

Beneficial bacteria break down ammonia. As already explained above, ammonia lessens toxicity by breaking down into nitrites and eventually nitrates.

Later, during the routine water change, the nitrates are removed from the water. It is this kind of biological filtration that keeps the aquarium healthy and in balance.


Frequently Asked Questions (FAQs)

How Should Old Filter Media Be Handled?

Some used sponge filter media could be cleaned off and temporarily used again as a technique to transfer good bacteria to new media.

How Can I Replace the Filter Media in My Aquarium Without Losing Bacteria?

When installing a new filter, you can either change only half of the media at once or leave the old one in place for a while.

Can aquarium filter cartridges be reused?

No, you shouldn’t reuse it. Change the cartridge at least once every month or if you detect a significant drop in water flow


Even though maintaining the health of the aquarium’s inhabitants depends on regularly cleaning the cartridge filters, doing so should be rather simple. 

Maintenance cleaning could seem a little onerous, but all that is required is a simple rinse with water that will be thrown away. 

It is crucial to keep in mind that cleaning filters with hot water or detergent not only kill all beneficial bacteria present in the filter but will also reduce their useful lifespan.

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Arif H Fahim

Welcome to PetFishTank! My name is Arif. I make an effort to publish educational articles using my many years of expertise as a fish owner.

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