How Do You Change An Aquarium Filter Without Losing Bacteria

How Do You Change An Aquarium Filter Without Losing Bacteria

AquariaWise is a participant in the Amazon Associates program and a few other affiliate programs and may earn from qualifying purchases at no extra cost to you. However, we have vetted every program in this guide and believe they are the best for generating affiliate revenue. You can read our full affiliate disclosure in our privacy notice.

A common disadvantage of changing your aquarium filter media or cartridge or even the whole unit is losing bacteria that establish inside the filter. These beneficial bacteria are responsible for keeping ammonia, nitrites, and nitrates out of your fish tank. And in their absence, your water quality will crash leaving your fish vulnerable to ammonia poisoning.

So how do you change an aquarium filter media or cartridge or even the whole unit without losing these beneficial bacteria?

Well, you’ll need to make sure the bacteria from the old filter media colonize the new filter media or cartridge before you put it in the tank.

To do this, either leave the old filter media in with the new one, reuse the old filter media with the new filter for a month, or colonize the new media by running two (2) filters concurrently. One of the filters should have the old media and the second one with the new media.

One other way to make this work, is to remove debris from the old filter media and leave it inside the tank for a short while for the bacteria to spread across your tank. During this period, you can also run your filter with the new sponge to help beneficial bacteria establish.

Keep reading for more insight on how to change or clean an aquarium filter without losing beneficial bacteria.

How Changing Your Filter Leads to Loss of Healthy Bacteria

To best understand why it is ever so important to make sure an aquarium filter change does not result in the loss of healthy bacteria, it’s imperative that you first know what these bacteria are and how changing your filter affects them.

See, filter and bacteria are the life of an aquarium, without either of the two, fish would not survive in tanks. Filters trap solid waste and aerate your water aided by an air pump if you’ve got one, while bacteria breakdown harmful fish waste.

Initially, the fish waste is mostly ammonia, which if left in the aquarium, will cause ammonia poisoning affecting the fish’s healthy, more so its respiratory system, starting with the gills.

The bacteria that develop in the biological section of the filter come in and breakdown ammonia into nitrite and then into nitrates, which are not harmful to tropical fish, albeit in large amounts.

For beneficial bacteria to develop in a new aquarium, the tank needs to be cycled, this way bacteria establish inside your tank and settle in the filter media ready to eliminate any harmful waste, either from fish poop, leftover food or plant debris.

So, when you change the filter in a mature tank, you also expel all the bacteria that formed when you cycled your tank leaving your fish susceptible to ammonia and nitrites poisoning.

That said, some beneficial bacteria do live in the substrate, but the health of your fish tank mostly depend on the bacteria in the filter, and that’s the reason why you ought to be careful when changing your filter.

This also applies when you have to clean your substrate or filter because healthy bacteria are also be lost this way.

How To Change Your Aquarium Filter

Knowing when to change your aquarium filter is quite important, but also how to change the filter because the actions you take will determine what happens to the nitrifying bacteria and the overall tank health.

For starters, you should never at any one time change all your filter media at once, and if you have more than one filter (media), don’t change them all at the same time.

Changing all filter media at once will interrupt the biological balance in your tank and the waste that your good bacteria is supposed to take care of remain in the water column and your fish start to get sick.

So, assuming your aquarium filter comes with two sponges or pads, which is highly recommended, then remove and discard each sponge at a time after making sure the other one has a well-developed bacteria colony.

A single filter pad is capable of holding enough bacteria to prevent any issues while the other one develops its own colony.

In case you only have one filter media, it’s better to replace only one-half of the filter media at a time. It is also advisable to have two filters in your aquarium in such instances. This way, you can have an old filter media in one of them while you change the media on other filter.

If you have more than one filter unit or media, do not wash them all at the same time. Instead, clean the filters a week apart to keep beneficial bacteria in the tank active at all times.

It OK to leave the old sponge in your aquarium for up to six (6) weeks to give the new one enough time to establish.

During this period, continue with the regular water changes and clean your aquarium as you normally would. Also, keep an eye on your water parameters, including ammonia and nitrites levels, which should be kept at zero (0).

Nitrates are not too harmful as long as you keep them below 20ppm; Adding plants in your aquarium should help with excess nitrates.

Also monitor the ph in your fish tank, making sure it remains within the range of the fish you have. A range anywhere from 6.0 to 7.5 is fine for most tropical fish. 5.0 is also not too bad for fish that prefer slightly acidic water, whereas 8.0 is perfectly OK for species that like things on the alkaline side.

How to Clean Aquarium Filter Without Killing Bacteria

Away from changing your aquarium filter, you can also lose healthy bacteria by cleaning the filter media or cartridge. However, depending on the type of filter you have in your fish tank, there is a way to clean it and still protect the bacteria.

An easy way to do this is rinsing (instead of washing) your filter sponge or pad in old aquarium water inside a clean bucket, making sure you remove any solid debris, uneaten food or fish poop that sticks on there to avoid reintroducing waste into your fish tank.

In view of the fact that your aquarium filter media house the beneficial bacteria that can easily be dislodged (as I’ve mentioned before), only squeeze your pads and sponges gently and roll them between your hands to remove the dirt, but not the bacteria.

Also, there is no need to wash your aquarium media if you don’t have to. Only clean the pads when they are visibly dirty or if you notice a reduction in their efficiency.

Just as much, avoid shocking the filter by cleaning the media in aquarium water, and not hot or cold water. Tap water can be used if you are sure the water does not contain salts, metals or chemicals like chlorine which are harmful to tropical fish.

What Else Can Kill Healthy Bacteria in Your Filter?

As I mentioned before, cleaning your aquarium filter could also result in the loss of healthy bacteria in a fish tank, same as turning off your aquarium filter and air pump or if the equipment goes off because of power cuts.

This is so because the good bacteria in fish tanks are aerobic, meaning they consume oxygen, which they get when the filter or air pump aerates the tank.

Other factors with the potential to kill the bacteria include fish medication and cleaning your aquarium wholesomely.

Fish medication contain chemicals harmful to nitrifying bacteria, whereas your substrate house some of the bacteria that don’t settle in the filter.

For this reason, if you decide to empty your aquarium for a complete substrate wash (maybe because of excess algae or a pest snail problem), make sure you leave a chunk of the gravel unwashed to help reestablish the bacteria once you place the substrate back into the tank.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

Author image

AquariaWise Newsletter

Get exclusive the tips, that we only share with our subscribers. Enter your email address below.

Your subscription could not be saved. Please try again.
Your subscription has been successful.

This site uses cookies. By continuing to browse the site, you are agreeing to our use of cookies. Okay, thanks