How does a Fish Tank Filter Work

How Does a Fish Tank Filter Work? Read This First!

We are reader supported. When you purchase through links on our site, we may earn an affiliate commission. Also, as an Amazon affiliate, we earn from qualifying purchases.

One of the most crucial components to having an aquascape in your home is the filter. These help keep the tank clean, removing debris, toxins and other poisonous compounds from the water. It mitigates odors, maintains stable water parameters, creates a water current for fish and lowers harmful waste.

But, how does a fish tank filter work? We’ll detail how they use or combines chemical, mechanical and biological filtration media to clean and remove debris. These work to keep ammonia and nitrite spikes at bay along with oxygenating the tank via water flow.

Knowing how a fish tank filter works is imperative for any aquarist, regardless of experience level. This will help you find the right kind for your particular fish while being able to handle the job effectively. Getting the wrong filter is one of the worst things you can do for your aquatic pets.

What Does a Fish Tank Filter Do?

Fish tank filters reduce and mitigate manual maintenance. It effectively and efficiently purifies the water, keeping it free of harmful chemicals that can harm fish. This includes things like feces and uneaten food. It keeps the water parameters stable without too much fussing over it from you.

Plus, it provides a nice current for fish, which is useful depending on the species you have. Some fish, like goldfish, love a stronger current in which to swim and frolic. Others, like Siamese fighting fish, prefer things a little calmer with a barely-there kind of water flow.

Overall, fish will be able to breathe, play, explore, eat, sleep and live better because of the clean water provided by the filter. You won’t have to clean the tank nearly as often as well.

What Are the Various Types of Fish Tank Filters; How Do They Work?

There are three basic types of fish tank filters: biological, mechanical and chemical. Some are in a single type or they can be a combination of two or all three. Regardless, all of these remove tank waste, which help to maintain the beneficial bacteria brought on from the nitrogen cycle.


When your fish emits waste from breathing, defecating or not eating all their food, this increases ammonia levels and other impurities. Biological filtration removes this by breaking down ammonia and nitrites, transforming it into nitrates.

It’s able to do this due to the beneficial bacteria provided by the filtration media and the nitrogen cycle. Therefore, biological filters take what’s already present and processes it into something usable for fish. 


The next type of filtration is mechanical and it also incorporates the use of beneficial bacteria via its media, which is usually a sponge, foam an/or matting. This provides a physical barrier to prevent particles, debris and other substances from infiltrating the tank.

Mechanical filters capture these impurities and trap decayed material in multiple stages. The largest particles trap into the sponge or foam. The mesh layer of the next sponge in the contraption refines the capture of waste and debris. The last stage is usually a piece of wool, which catches the smallest pieces possible.

However, you have to clean this type of filter on a monthly basis and you can’t use tap water for it. When you do your partial water change, take a bucket of the aquarium water and use that to clean your mechanical filter. You never want to get it squeaky clean so you don’t lose that layer of beneficial bacteria.


Because keeping an aquarium is essentially an exercise in chemistry, the chemical filter removes any and all kinds of toxins within the tank. Excess proteins or extra nutrients can buildup inside, contributing to ammonia and nitrite spikes along with throwing the pH balance out of whack.

So, adding something like chlorine will absorb these harmful compounds. Chemical filters also incorporate activated carbon, which will require frequent replacement. But it removes discoloration and odors in a very reliable way.

Which is the Best Type of Filtration for a Fish Tank?

The type of filtration best suited to your particular aquarium will depend on how much space you have, the size of your tank, the water parameters required by your fish and the number of inhabitants that live in the tank.

For example, smaller tanks with one or two fish may go with a single type of filter, such as biological or chemical. But, large community tanks would do well to have a filter that incorporates all three types. Simpler models may not provide enough water flow and oxygenation while big, all-encompassing types might provide too much water current.

What Should You Look for When Buying a Fish Tank Filter?

The main factor to consider for a filter is your fish. Understand what their feeding and digestive habits are. Then, you’ll want to consider the size of the tank you have along with how you want to install the filter into the aquarium.

Filter Installation Methods

The fish tank filter market is huge, which mean there are many styles. Some will work beautifully in your tank while others will not be sufficient. However, thinking about how you want to install it will help whittle down the options.

  • Hang On: A hang-on or hang-on-back is a power filter that often clips onto the side of the aquarium. It can incorporate one, two or all three types of filtration. These are very strong and efficient, which makes them idea for large tanks and strong water flows.
  • Internal: Ideal for fish that prefer still water and smaller tanks, internal filters are submersibles that go right inside the water. These are often compact and discrete. However, this can take up considerable real estate within the aquarium, which can cause some fish species stress.
  • Canisters: Canister filters are another type of powerful filtration that can provide a nice current within a tank. These rest under or outside of the tank and create the best water flow with the ability to cycle hundreds of gallons of water per hour. Therefore, it’s only good to use in a large communal aquascape.

Other Considerations

Irrespective of the type of filter or installation method, there are several other aspects in deciding what kind of a filter to get. In essence, it should be efficient and convenient with two or all three types of filtration.

  • Adjustability: One of the biggest of these is adjustability. No matter what your fish prefer, you want to be able to control all the components of the filter to ensure the ultimate comfort for your scaly friends.
  • Power: Also, make sure that the filter will be powerful enough to clean your tank. Referring to ones from longtime trusted brands is the only way to ensure you’re getting a quality product. But, it should match the size of your tank. For instance, your five-gallon tank doesn’t need a high powered filter with all three types.
  • Simplicity: Yet another consideration should be simplicity of use and operation. If you’re new to fish keeping, don’t get a filter that’s difficult to setup or its configuration is something akin to operating a spaceship. You should be able to understand how it works with an ability to change filter media quickly.