What's the Difference Between Aquarium Filters? - Chemical, Biological and Mechanical Filtration for Beginners

Posted by sharon seals on

A commonly asked question of the beginning aquarist is how filtration works and what size of filter is needed. A quick cruise down the filter aisle of any fish store gives hints to the reason why they may be asking. The options are endless, and not even the most advanced hobbyists could tell you everything about a filter system without doing their due research.

In the beginning, you aren't going to have any fancy fish or coral that need specific parameters and extreme filters, it’s once you get into the more advanced stages that you come to the conclusion that you are going to start needing to do a little something more for your fish. That is when you realize, not only are there hundreds of different filters and sizes, but even more ways in which they work. Each filter is designed to perform a specific method of filtration, and some might do multiple. Prices vary based on what the filter does, how easy it is to use, and how effective it is. 

(One of the best canister filters we have, the Fluval FX6 employs Smart Pump Technology to self-monitor itself and provide mechanical, chemical, and biological filtration.)

Three Methods

Chemical, biological, and mechanical filtration are the three different methods used to keep your tiny ecosystem clean and healthy. It is critical to know the difference if you want to get serious with your watery pets and keep them alive. Mistakes are very common at this stage in the process but don't let one failed cycle get you down, we all do it. Take solace in knowing that the longer you are into the fish hobby, the easier it gets to realize what you are needing, lacking, or maybe need to change when it comes to your filtration system. From there, you can start shopping around for the best filter for your aquarium setup.

Chemical Filtration

Chemical filtration is the use of filtering media within the filter area that are meant to capture and extract the harmful chemical compounds from the water. Chemical resins will perform this task, but mostly activated carbons are used. This method isn't necessary but can be helpful when needing to add an extra level of protection in certain circumstances, such as after a medication treatment.

(Aquarium packages are perfect for the beginning aquarist as they come with a little bit of everything to get you started in fishkeeping. While you don't always have to add chemical filtration, most beginner filters do include activated carbon to ensure you have a well-rounded system.)

Chemical filtration is used as an add on as it can’t work alone. For example, adding carbon to a large reef system will help remove any toxins that certain corals may release under stress, the coral wouldn’t be alive without biological filtration already in place though.

A great example where you commonly see carbon in use is when a beginning aquarist, or anyone purchasing a kit, takes out their prepackaged bag-like filters. You'll notice that they are filled with little pieces of material, these pieces are carbon. The filters will work in most systems, though other forms of filtration are at play and necessary to make them effective.

Mechanical Filtration

Mechanical filtration refers to the process that goes on inside a typical filter as it sucks up excess waste and organic material. These materials are blocked by the filter sponge and need to be cleared off on a regular basis to prevent buildup. If excess wastes were left to soil up the tank, they would settle to the bottom and build up harmful levels that would be bad for your tank environment.

Many aquarists like to use a variety of sponges to filter out larger and smaller compounds within their tanks and ensure their water is crystal clear. As the waste builds up on these sponges within your filter, you will also notice bacteria beginning to grow. This is beneficial and part of the biological process. In using a variety of layered sponges, you are actually creating different environments for all forms of bacterium because of the access that the top layers have to air and the lack thereof at the bottom tiers. When you layer your media, you are essentially creating a tiny biosphere within your filter compartment.

Take care with these bacteria growths as they are helpful to your tank, and always wash media in excess aquarium water that has already been cycled. Do not rinse anything under the tap as tap water often has trace amounts of chlorine that will kill beneficial colonies, which is often why carbon is added to a beginner's filter too!

Keep in mind that mechanical filtration does not filter out other harmful materials as carbon does, but it is necessary in order to maintain a healthy aquarium.

Biological Filtration

Biological filtration is the natural process that an environment of any form, big or small, goes through. In the wild, this comes naturally, but in a small tank environment, the process may take some time.

Biological filtration uses beneficial colonies of bacteria to filter out ammonia and nitrite from your aquarium. These harmful substances, when built up, become poisonous and will crash your aquarium and kill the inhabitants. The bacteria colonies grown in the process of biological filtration live off of these substances though, and as they process them, they are converted to nitrate, which is safe for your aquarium.





(Biological filtration can be enhanced in many ways, including through the use of eco substrate and plants. We like to use Fertility Substrate to aid in plant growth.)

Biological filtration occurs naturally in the tank, especially if you grow plants or have a reef, but you have to create it first. The process when first setting up a tank is known as cycling and can take up to six weeks before your aquarium is growing these natural colonies. Cycling takes a little skill, but once you get the hang of it you'll find ways in which to speed up the process, like by adding some hardy plants. Patience is key here as you don't want to introduce fish too soon or they will die from the stress.

Biological filtration occurs even in the simplest of tanks, however, the process is made even better by adding filtering media, such as bio-balls, to a canister filter or other type of system. These forms of filter media are made specifically with surface area in mind as the more room for growth there is on each piece of media, the more filtration there is available. Do some research about using media and the different types before jumping in and buying a bunch though. All have their benefits and disadvantages, and although extra material never hurts your tank, some might work better for your setup than others.

What is Best for Your Tank

Biological and mechanical filtration are essential to a healthy and thriving aquarium. Chemical filtration may or may not be beneficial, though extra filtering of any sort never hurts. The filtration system is the heart of your aquarium and not to be left aside with the thought that you’ll be fine until you figure it out. Unless you have a very basic tank, you will at some point want to upgrade if you begin to add to your bioload. The chances that you've gotten by just fine without a little filtration knowledge so far are very slim. If you've never accidentally killed a fish or two, then congratulations, you've gotten lucky!

Start with what you know and work from there. Many aquarists go their entire lives without using anything but hang on back filters. These work great but aren't for everyone. Our advice is to start small, research beforehand, and don't give up just because of one or twelve failed attempts, you'll figure it out eventually!

Our Personal Favorite

The ultimate in filtration systems, in our opinions, is the sump setup. Though we do recommend starting with something like a canister setup first. Sumps house all components of the tank and provide for all levels of filtration, you can also get creative in how you want them to work. You may or may not even wish to add a refugium as a small side tank depending on what you have within your aquarium. Sump setups are better for the advanced aquarist, though any hobbyist can never start learning too early when it comes to enhancing their filtration system!


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