How To Change Aquarium Filter Without Losing Bacteria – 3 Effective Methods

If you’re keeping fish for a while, you have probably come across the word ‘beneficial bacteria.’ In an aquarium environment, fish wastes and other organic matter decompose and form harmful ammonia for fish.

Bacteria help to convert ammonia into nitrite and nitrates and eventually make the water livable for the inhabitants. 

Without bacteria, you can’t imagine a conventional aquarium. However, bacteria develop over time, and it’s been recommended to allow 3-4 weeks to establish bacteria colonies in your tank before adding fish. The process of growing bacteria is called the nitrogen cycle

Bacteria need some sort of media to grow. Aquarium filter contains bio-media to colonize bacteria. But those bacteria can be lost during cleaning/changing the filter cartridges (only if you do it improperly) or if you change the aquarium filter altogether.  

To help you out, here, I’ll discuss how you can preserve biological balance (keeping bacteria alive) and How To Change Aquarium Filter Without Losing Bacteria

How To Change Aquarium Filter Without Losing Bacteria?

Suppose your aquarium filter gets old and tired of keeping the aquarium clean. Now, you feel the urge to purchase a new filter. If you naively replace the filter, and you think you have done a great job, but all of a sudden, a problem starts that you never anticipated. 

The problem is that you lose all the bacteria which keep the water safe for the fish. I know, at some point, you have to change your filter, but you need to make the switchover as smooth as possible so that it does not impact your fish’s well-being. 

Here, I’ll suggest three ways to follow while changing aquarium filters but not losing bacteria. 

Method-1: Leaving The Old Filter In The Tank

The easiest and most effective way to prevent bacteria loss is to run both the old and the new filter parallel for a few weeks. The new filter will get ample time to build up beneficial bacteria from the old filter media if you run it in tandem. 

Method-1 Leaving The Old Filter In The Tank

The old filter should be removed after a month (or 04 weeks). During this period, bacteria will be colonized on the new filter media.

However, following this method, you should be careful about the flow rate. Keeping two filters at a time may increase the flow rate (water circulation). Therefore, you must keep a close watch on the flow rate when two filters are in operation. 

The disturbance caused by the high flow rate increases stress levels for the fish in your tank and can even cause injury or death to those most vulnerable: fry and small fish. Moreover, fish that aren’t good swimmers may push toward the corner because of increased current. 

Method-2: Reusing The Old Filter Media

What if your aquarium filter stopped working and the filter pump is not functioning? Moreover, if you don’t have an option or don’t like to run both filters at a time, here comes the second method. 

Method-2 Reusing The Old Filter Media

The second method is to use the old filter media with the new filter because most bacteria grow on the media itself. So what you have to do is remove the media from the old filter, install it in the new one, and run it for four to six weeks. By this time, a sufficient amount of bacteria will have accumulated on the new filter.

The one downside of this method is that the old filter cartridge has to fit in the new filter chamber. If the new filter is of a different shape or bigger size, you might not be able to use the old one in that new setup.

You should also carefully examine an old cartridge before reusing it; if it’s broken off or falling apart, don’t put it back into action!

It also depends on the types of aquarium filters you use. This method only applies if you use a canister, HOB (hang on the back), or internal submersible filter. These types of filters provide three-stage filtration and use separate biological media to enhance bacterial colonization.  

Therefore, in that case, if you upgrade your aquarium filter, you can use some of the biological media (ceramic rings, bio bags, bio foams, etc. ) from the old filter in the new one. 

Method-3: Colonizing The New Filter

If you don’t want to run two filters at a time and old filter cartridges do not match the size and shape of the new filter you bought, this third method is for you. 

Method-3 Colonizing The New Filter

When removing the old filter, take out its cartridges and place them inside the aquarium with the new filter in operation. It will work similarly to fitting the old cartridges in the new filter. But check the condition of the media, and make sure it’s in good shape to use.  

Continue for a month in this way, and over this time, the new filter will be colonized with the beneficial bacteria. After that, simply remove the old cartridge from the aquarium.

Above mentioned three methods are equally effective and practiced in the fish-keeping community. You can follow whatever suits best for you.

Once the transition period is over, keep monitoring the tank parameters to ensure everything is in range for your fish to live happily and healthily. 

How To Change Aquarium Filter Cartridges Without Losing Bacteria?

Suppose you are not replacing the aquarium filter; instead, you are changing filter cartridges or media. In that case, too, you may end up losing all the bacteria if you do that incorrectly. So, you need to know how to change aquarium filter cartridges without losing bacteria.

What If You Use A Sponge Filter? 

If you use a sponge filter, and the sponge no longer springs back into the proper shape, then probably it’s time to replace the sponge element. 

If the filter has two sponges (recommended), then it’s straightforward. You can remove and discard the whole sponge and replace it with a brand-new one.

Enough bacteria will remain on the other sponge unit to keep everything stable in the aquarium and help the other one colonize the bacteria. 

How To Change Aquarium Sponge Filter Cartridges

The job gets a little more complex if the sponge filter consists of only one sponge. The reason is, that you cannot remove the sponge from the aquarium. If you do that, you will lose a significant amount of bacteria. 

Therefore, instead of taking out the old sponge, you need to find a way to keep that inside your aquarium.

While at the same time, you are running the sponge filter with a new sponge unit. That’ll help to grow bacteria on the new sponge; after one month, you can remove the old sponge. 

What If You Use A Three-Stage Filter? 

A three-stage filter has different filter media for mechanical, biological, and chemical filtration. Usually, sponges perform the mechanical job, bio-media do the biological part, and activated carbon works chemically to deliver the desired water conditions.  

How To Change Aquarium Filter Cartridges - 3 Stages

The mechanical sponge can be removed and replaced with the new one regularly because bio-media stores a significant amount of bacteria; therefore, changing sponges will not impact. 

Whenever you change the bio media, always do that in half a portion at a time; otherwise, you’ll lose all the bacteria present in the biological chamber.

If you replace the entire portion, make sure you have matured mechanical sponge media in place for backup. However, carbon media can be changed at any time because it doesn’t function biologically. 

Does The Aquarium Filter Cartridge Really Need Changing?

There is really no need to change the filter cartridge unless it does matter. Cleaning and maintenance are essential for aquarium equipment to function correctly. However, some people make the mistake of changing the filter cartridges during every scheduled maintenance. 

Changing filter cartridges unnecessarily costs you more money and increases the chance of losing bacteria. So now the question is when to change a filter cartridge. If you see that it is torn out or falling apart and is not usable anymore. 

Therefore, decide carefully before changing the cartridge, and find out if it really needs to be changed. Since it doesn’t make sense to risk losing beneficial bacteria and stress out your fish because of that. 

How To Clean Aquarium Filter Cartridges Without Losing Bacteria?

You may lose bacteria during cleaning of the filter media or cartridges as well if you do it incorrectly. Here, you can use a simple trick, never ever clean filter media in running tap water.  

Instead, I’ll suggest cleaning the media in your fish tank water. First, siphon out some of the aquarium water into a bucket using a gravel vacuum. After that, wash the media thoroughly, but don’t throw out the water. Rather, use a proportion of the water from the bucket in your aquarium. 

Yes, it may contain some dirt and debris; it will also carry the bacteria you would have lost if you discarded the water. However, your filter will take care of detritus (don’t be worried), and beneficial bacteria will remain intact in your aquarium following this way. 

You can also take tap water into the bucket and do the cleaning similarly. But sometimes, tap water contains chlorine to kill harmful bacteria. Also, there is no guarantee that it will not kill the beneficial bacteria for your fish. Therefore, I recommend treating the tap water before using it for aquarium purposes. 

What Are The Other Reasons To Lose Bacteria?

What Are The Other Reasons To Lose Bacteria

Cleaning or replacing the filter cartridge or changing the aquarium filter are not the sole reason. There are some other instances when you can lose the bacteria. 

If you have to treat a sick fish using medication that can negatively affect bacteria. Therefore, always test the water parameter after treating the fish and adding some beneficial bacteria. 

Bacteria need oxygen to grow and survive. So, suppose there is a low oxygen level for an extended period (more than 2 hours) during a power cut. In that case, that can destroy the bacteria colony. Therefore, it is a good practice to be aware of such situations beforehand to take action during power outages. 

You can use a battery-operated air pump as a backup. Also, there are some natural methods to add oxygen to your aquarium during an emergency period. 

A Common Misconception On Aquarium Filters And Bacteria

Some people believe that good bacteria only live inside the aquarium filter; bacteria elsewhere are bad bacteria and can be removed. But it’s not necessarily true; bacteria can grow on almost anything, which provides surface area for them to colonize. 

Filter sponge, ceramic rings, or other bio-media provides a large surface area to expedite the bacteria colonization. And yes, filter media contains most of the good bacteria, but there are other places like decors, glass, gravel, driftwood, etc., where bacteria can also be found. 

Therefore, during cleaning or changing the cartridge or the whole unit result you lose a significant portion of bacteria which can lead to a biological crash. However, if bacteria present in some other places are sufficient, that might save you from the disaster. 

But you should be cautious and perform the cleaning or changing tasks correctly. 

Wrapping Up

Bacteria are microscopic creatures and can’t be seen by the naked eye whether they are doing their jobs perfectly or not. So, it’s always to test the water parameter after changing aquarium filters or cartridges. 

Hopefully, you’ll never have any issues if you follow the guidelines and some of the best practices I outlined above on how to change aquarium filters without losing bacteria. 

 I would like to hear your thoughts on the topic; please leave a comment below.

Sujit Modak

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