How To Change Aquarium Filter Without Losing Bacteria?

how to change aquarium filter without losing bacteria
An aquarium filter is responsible for cleansing the water in your tank, and over time, the filter grows helpful bacteria that it circulates throughout the aquarium. Unfortunately, when you change your filter, you can lose these beneficial organisms, which can be detrimental to the health of your fish.

To change an aquarium filter without losing bacteria, run the new filter alongside the old for a few weeks, colonize the new filter using media and bacteria from the old, or run your new filter through a nitrate cycle in a fishless tank. Since some fish are more sensitive, test the pH levels often.

This article will discuss four methods you can use to replace your filter without losing bacteria. We will also go over how to encourage faster bacterial growth on your new filter to keep your aquarium thriving.

Contents

Why Do You Have To Preserve the Good Bacteria in Your Tank?

Marine life release ammonia from their gills and feces that can disrupt the biological balance of your aquarium if left untreated. A filter is used to help moderate this, and the good bacteria it produces helps your fish in their nitrogen cycle by oxidizing any harmful chemicals into gentler nitrate.

Without nitrifying bacteria, your aquarium becomes uninhabitable to fish and plant life. For this reason, you have to prevent the loss of the established bacteria in your tank to avoid interfering with the cycle.

Before you introduce your fish to a new aquarium, it is essential to run your filter and allow the water to acclimatize. During this process, you will need to introduce chemicals and monitor the pH levels within the water. As certain species can be sensitive to pH changes, it is vital to change your filter properly in order to maintain the balance of bacteria within the water.

If you are looking to upgrade your filtration system, Ha Y N Fish Keeper has a video going over ways you can enhance your filter for maximum bacterial potential:

4 Methods To Change Your Filter Without Losing Bacteria

It is essential for your tank’s health to keep the old filter on hand. Despite it being faulty or out of date, the old filter can still supply your replacement filter with its bacteria. Here are the ways you can stop the loss of bacteria during your transition to a new filter:

#Method-1: Run the Old Filter and New Filter Together Before Removing

A new filter will guarantee you a cleaner tank, but without enough bacteria, your fish will suffer from the new system. For this reason, you must maintain the levels of bacteria that existed before, and running your old filter with the new one is the most effective way to stop bacteria loss.

Keep the old filter in the tank for four to six weeks alongside the new one. In this time, the new filter will accumulate a sufficient amount of bacteria to support the tank’s needs.

The only drawback to this method is that two filters will increase the tank’s flow rate and some species may not be able to handle the added movement. Research your fish to see if you can safely operate two filters in your aquarium.

#Method-2: Colonize the New Filter With Bacteria From the Old Filter

Most filters include a cartridge that houses some of the bacteria used in biological filtration. You can use this cartridge to encourage bacterial growth in your new filter.

Remove the cartridge from your old filter and add it to the replacement filter. After one month, the new filter will have enough bacteria for you to upgrade the cartridge. If desired, you can keep the old cartridge attached without harming the filter or your tank.

#Method-3: Recycle the Old Media in the New Filter

Your filter contains tank media (the filter’s contents used to change the water’s qualities), which can be reused. These may include:

  • Bio-rings
  • Sponge
  • Ceramic rings
  • Foam pads

Instead of throwing them out with your old filter, reuse them in the new one. The majority of the bacteria your aquarium thrives on is stored in the filter media. Therefore, recycling them in your new filter will keep most of the bacteria intact.

What To Do When the New Media Doesn’t Fit?

If you have upgraded your filter to a new size, the old media may not fit inside. If this is the case, keep the used media as close to the filter as possible. It’s just as effective as adding the colonized media inside the replacement. The good bacteria can still make their way to populate your new filter faster at a close distance.

#Method-4: Put the New Filter in an Empty Tank First

If you’re going to replace your filter within the next few months, start cultivating your new filter early to avoid having to run two filters at once. You can grow a colony of beneficial bacteria on your new filter before fish ever interact with it. When you make the switch, you will preserve your bacteria levels.

However, you can’t run the filter in the aquarium alone and expect the bacteria to form. This method is the same as the one required to start a new aquarium environment. In this case, add some filter media and perform the following steps:

  1. Fill your tank with water and calculate its volume.
  2. Use a liquid test kit to examine nitrate, ammonia, and pH levels. Write down the results.
  3. Add ammonia to your aquarium.
  4. Power on your filter.
  5. Wait three days and test the ammonia levels again. If the ammonia content is below 2ppm, add more.
  6. Repeat step 5 for four to six weeks.

After six weeks, the new filter will be ready for your main fish tank.

Why Is Your Aquarium Cloudy After Changing Its Filter?

how to change aquarium filter without losing bacteria
Many aquarists report murky tank water shortly after introducing a new filter in their tank. This cloudiness is called bacterial bloom and can start two to three days after changing your filter. In most cases, this condition is not hazardous to your tank. Therefore, there is no need to change the water when you notice it.

Seeing bacterial bloom is a sign that beneficial bacteria are multiplying at high rates. In two to five days, the water will clear on its own. However, if the condition lasts for more than a week, there is a severe bacterial disease.

How To Know If Your Filter Change Decreased Bacteria?

Despite your efforts to prevent the bacterial loss, there are still reasons why your new filter may cause a decrease in bacteria. If you notice the following after your filter change, there has been a drop in bacteria levels:

  • Constantly sleeping fish
  • Fish are refusing to eat
  • Reddened gills are appearing
  • Fish are rolling over randomly
  • Sudden deaths
  • The tank inhabitants stay at the surface of the aquarium
  • Bloody veins show up on your fishes’ skin

If your new filter disrupts the biological balance in your aquarium, encourage bacterial cultivation through healthy practices like improving your tank’s oxygen capacity.

How Often Should Aquarium Filters Be Changed?

You should only change your filters if they are broken or start producing toxic water. It is best practice to change your filters sparingly to assist your marine life’s bacterial needs. Moreover, tank filters can last for years; therefore, regular replacements are unnecessary.

Suppose you have noticed that your filter doesn’t run as efficiently. In that case, before changing your filter, try rinsing it in some of the tank water to remove excess dirt. For some, this will restore your filter’s functions to a better condition.

It Is Not Necessary To Change the Filter Cartridge

When changing your filter, you can keep the old cartridge. It is not necessary to change the filter cartridge unless it is damaged. Aquarists can reuse the cartridge to help maintain bacteria in their aquariums. Filter cartridges can last years once they are in good condition.

It is essential to remember that all tanks need some biological filtration. A new cartridge cannot decompose the harmful ammonia inside your tank. It is better for your fish when you reuse as many pieces from the old filter as possible.

What Happens When You Don’t Change the Filter?

As mentioned, tank filters last for an extensive period. Many aquarists believe that they do not need to be changed at all. While it is not necessary to change your filter, there are disadvantages to continuously running a filter past its usefulness.

Some filters can become extremely clogged, which restricts water flow throughout the media. Given this, bacteria cannot flow efficiently through your tank.

When running your filter, perform regular inspections to ensure you aren’t allowing excess dirt to block your filter. Be sure to also clean and rinse the filter at least once a month.

What To Avoid When Changing Your Filter?

Seeing that a new filter can be unhealthy for your tank, there are two practices you’ll want to keep in mind whenever you change your filter:

  • Do not remove all the filter media at once.
  • Replace the filter as quickly as possible.

Never Remove All of the Old Media at the Same Time

If you are removing the filter media, never remove all of them at once. Changing all of the materials at the same time interrupts the biological balance in your aquarium. This environmental disruption puts your fish at risk of catching diseases.

Consider replacing the media one by one over a few weeks. Alternatively, you can change half of the filter media and add the other half in one month. This method allows the new media to develop bacteria quickly.

Always Have a Filter in Your Tank

It is always best to have a filter running in your tank. Otherwise, your fish will be swimming in detritus, fish excrement, and other health hazards.

For this reason, try to add your new filter to the tank while your other filter is still in operation. But if your fish can’t handle the increased flow rate, replace the filter as quickly as possible. Most fish cannot survive in a tank without a working filter for more than three days.

Do not remove your old filter until you have the new one readily available for your aquarium.

How Long Can Your Aquarium Not Have a Filter?

In most cases, the filtration system in your aquarium has to be powered down and removed to replace the filter. You should not leave your aquarium without a filter for more than 12 hours. However, after eight hours, your fish will start getting damaged by the high ammonia and nitrite levels in the tank.

A home replacement won’t take hours to do, and your fish will be safe throughout the process. Remember that the filter bacteria starts to die after thirty minutes, so it’s best to work fast.

It is mostly power outages that pose a real threat to your aquarium’s health. In case your filter malfunctions or your household is without power for a few days, take these steps to keep your fish healthy without a filter:

  1. Change the water every 12 hours.
  2. Regulate feeding to decrease nitrate levels.
  3. Feed sparingly to decrease fish waste which will end up overcrowding the tank.
  4. Cover the aquarium.
  5. Keep nitrates below 20 ppm, with 0 – 10 ppm being the ideal nitrate levels.

How To Increase Bacteria on Your New Filter?

Once you’ve successfully changed your filter, you will need to ensure that it’s colonized with bacteria quickly. Some marine life in your tank depends on these bacteria for things like:

  • Removing toxins
  • Keeping the water clear
  • Breaking down dead plants

As mentioned, these bacteria take time to cultivate. Still, there are nine things that aquarists can do to encourage bacterial growth:

  • Enhance oxygen levels
  • Ensure that the water is warm
  • Occasionally place your tank in the dark
  • Leave the filter running continuously
  • Use an ammonia source
  • Include filter media
  • Have a high flow rate
  • Feed your fish more food
  • Keep the capacity of your aquarium low

Enhance Oxygen Levels

Improving the oxygen levels in your tank improves bacteria levels. The bacteria require oxygen to function and break down nitrite and ammonia. But when adequate oxygen is not available in the tank, the environment isn’t suitable for bacterial functions.

To increase oxygen levels in your tank, consider the following:

  • Add an air pump
  • Stabilize the pH balance in your aquarium
  • Increase water flow
  • Raise the water’s temperatures by finding out the highest temperatures your fish and plant life can tolerate
  • Remove the aquarium cover
  • Use a fan for blowing air over your aquarium

Why Use an Air Pump?

Air pumps send bubbles throughout your tank. This action ensures that your tank has a healthy concentration of oxygen. They also force water through the filter, assisting cleaning and the movement of bacteria. Combining your new filter with an air pump helps enhance bacterial levels and circulation.

How To Stabilize the pH Levels in Your Aquarium To Improve Oxygen?

There is not a standard pH level that suits all fish tanks. If the aquarium houses saltwater species, the pH should be 8.0 or above. In contrast, freshwater fish prefer a pH balance of 7.6 and below. Inadequate acidity levels discourage bacterial growth on your new filter and will ultimately harm your fish.

Before adjusting the alkaline levels in your tank, research your species, then test the water for its present acidity. Afterward, you can decide to increase or lower the pH levels.

To raise pH levels, experts suggest adding driftwood to your tank water. On the other hand, making your tank more acidic requires reverse osmosis and a calcium carbonate-base substrate.

How To Increase Water Flow in a Tank?

Water circulation supplies your tank with oxygen. The higher the flow rate is in the tank, the more oxygen is provided. To increase the water circulation and improve bacterial growth:

  • Use a powerhead in your tank
  • Add air stones
  • Include a water pump in your aquarium setup
  • Get a wavemaker

Keep Your Tank Water Warm

Hotter aquariums cannot hold as many bacteria as cooler ones. At the same time, an aquarium that is too cold does not support biological filtration either. Beneficial bacteria multiply the fastest in water temperatures between 55 to 90°F (12 to 32°C).

If it is safe for your fish to remain in these temperatures, keeping your new filter in warm water will improve its bacterial colonization.

Put Your New Filter in a Shady Room

Bacteria grow best in the dark. Therefore, it will significantly help your new filter if you keep the light off sometimes. Ensure that your tank is also away from windows as sunlight reduces the bacterial growth rate by 50%.

When doing this, be mindful that light is essential to the cleaning and maintenance of your tank. To protect your fish, you shouldn’t keep the aquarium in the dark constantly.

Always Have Your Filter Running

Your filter has the fundamental ingredients required for rapid bacterial growth: a robust water flow and low light. Therefore, the longer your filter is circulating the water, the more opportunities for beneficial bacteria to grow.

Additionally, keeping your filter running all the time improves the oxygen levels around it. In turn, more bacteria develop around the new filter.

Add an Ammonia Source to the Aquarium

By adding a source of ammonia to your aquarium, bacterial growth improves to process the ammonia into nitrate. Your new filter and its media will be the warehouse for most of the bacteria formed due to the addition.

It is important to remember that ammonia is toxic to your tank. If you plan on adding enormous amounts of ammonia, consider using a fishless cycle to cultivate the new filter.

Some ways to improve ammonia levels in your aquarium include:

  • Adding more fish food
  • Putting old tank water with your new filter
  • Using household ammonia
  • Getting a tank-maturation kit

Use Filter Media

Filter media is essential for the health of your aquarium. They help to maintain the nitrogen cycle, which keeps your marine life alive, and most importantly, they house bacteria.

There are three kinds of filter media available on the market:

  • Biological
  • Chemical
  • Mechanical

Your tank should have biological and mechanical filtration at least. But it is best to combine all three to maximize bacterial growth.

There are many biological media available like:

  • Ceramic rings
  • Pellets
  • Foam
  • Balls
  • Sponge

When choosing your media, consider their resistance to wear, absorption, and stability.

Which Filter Media Grows the Most Bacteria?

Large biological media with lots of surface area can support the most bacterial life, allowing for a synergistic relationship between various bacteria leading to enhanced growth rates.

While you can also include smaller media tools in your tank, your aquarium’s biological balance will benefit most from more oversized items.

Have a High Flow Rate

Aquarium bacteria get their food from the water circulating in your tank. Improved water flow supplies the bacteria with more nutrients and oxygen to thrive. As the water pressure rises, the ammonia and nitrate levels in the water cause the bacteria to multiply.

When putting in your new filter, boost the flow rate but keep your fish in mind during this process. High water movement can give the fish more current to fight against and tire them out. Instead of putting your new filter in a populated tank, use a spare aquarium for this project.

Feed Your Fish More Food

how to change aquarium filter without losing bacteria
Cycling is the growth of an established bacterial colony. On average, it takes about five weeks for cycling to end. To enhance cycling on your filter, more waste must be inside your aquarium.

Bacteria is dependent on the waste content of your tank. These life forms sustain themselves on fish waste and need these nutrients for reproduction. The most straightforward method for improving waste production in your tank is by increasing the fish’s meals. It is best to raise their feed slowly as your new filter is not able to handle large waste amounts in its first few weeks.

Don’t Overpopulate Your Tank


As mentioned, new filters do not have an established bacterial system. Therefore, they cannot handle tanks with a lot of waste. If there are too many fish in the tank, the filter will be incapable of converting the toxic ammonia from the fishes’ waste.

Therefore, keep your tank at a manageable population. There is no standard for how many fish to keep in a tank, but Spruce Pets recommends that you use these calculations when stocking your aquarium:

  1. Multiply the length of your tank by its width.
  2. Divide the total by 12 square inches (77.42 square centimeters) for slender fish.
  3. For wider fish, divide the total by 20 square inches (129.03 square centimeters).

How To Instantly Add Bacteria to Your Tank and Filter?

To instantly improve the biological balance in your tank, add probiotic mixes in the tank after changing your new filter.

Probiotics help fish colonize bacteria inside their stomachs that maintain their health while other bacteria develop on the new filter. Including probiotics decreases the risk of harming your fish with your new replacement.

Moreover, these probiotics make their way into your tank water and further encourage bacteria’s cultivation on your new filter. Your fishes’ bodies and environment will benefit from the use of helpful external bacteria.

The most common mixes used in modern aquariums involve Bacillus and Lactobacillus. These bacteria have the following advantages for fish:

  • Improved digestion
  • Weight gain
  • Increased growth
  • Better feed conversion
  • Immunity boost

Admittedly, it will still take time for your new filter to have a stabilizing amount of bacteria. Still, your fish will be able to survive while the filter adjusts. Probiotic additives should be available at your local pet store.

How To Maintain Healthy Bacteria Levels in Your Filter?

Once you’ve got your filter to an acceptable biological level, you should do your best to maintain it. Even a slight decrease in bacteria can cause fish to die. Use the following tips to keep a biological balance in your tank:

  • Only change 10-15% of the water during cleaning.
  • Rinse your filter media in tank water.
  • Never wash all your media at the same time but rather work on specific pieces one week apart.
  • Always use dechlorinated water in your tank.
  • Avoid removing too much debris when cleaning, so you don’t wash away good bacteria.
  • Keep the filter media wet when it’s outside the tank.

Can You Have Too Much Bacteria in Your Tank?

Some replacement methods require using your old filter’s bacteria in conjunction with the new. This process can spark the concern of raising too many bacteria in your aquarium. While there are mishaps that lead to an overload of harmful bacteria, you can never have too many good bacteria.

The things that cause your tank to overload with deadly organisms usually have nothing to do with the filter or its replacement. These things include:

You will know when there are too many dangerous bacteria in your tank if you notice the following in your fish:

  • Inflammation
  • Continuous attempts to escape the tank
  • Rapidly moving gills
  • Constant rubbing against objects in the aquarium
  • Folded fins
  • Bloating
  • Fungus

In contrast, emphasizing the cultivation of helpful bacteria in your tank has no adverse effects.

What Kills Good Bacteria in Your Filter?

Many things cause bacterial death in your aquarium, but the most common reasons are fish medication and insufficient oxygen levels.

Some marine antibiotics will deplete the bacteria on your filter. For this reason, isolate the treatment of diseased fish to another tank. If you must treat the fish in an aquarium with a colonized filter, test the water after treatment for ammonia spikes.

Another threat to aquarium bacteria is low oxygen levels. Bacteria are aerobic, so oxygen is essential for their nutrition and bacterial functions. After only a few hours without oxygen, bacteria levels will decline.

In addition to performing your regular filter maintenance, be mindful of these two hazards in your tank.

Final Thoughts

Changing your aquarium filter can go wrong if you don’t maintain the tank’s biological ecosystem. If you don’t do it right, you run the risk of killing the healthy bacteria, which will directly affect your tank’s health. However, once you change the filter using the right methods that encourage bacterial growth, your fish and plant life will thrive.

Remember that even the smallest change in your tank’s pH levels can have adverse effects of certain species. With that in mind, always test the water and change your filter slowly, utilizing the existing bacteria in the tank.

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