Updated: October 6, 2020 - By: - Categories: Equipment

When you begin setting up your aquarium you know that you need to filter the water but there are many, many types of aquarium filter systems to choose from. In the tank? Outside of the tank? Small? Large?

Perhaps you already have a well established aquarium and you’re just thinking about upgrading your filtration. There are still many options and varieties to choose from and I have no doubt that this set of pages will be of use to you in making your selection.

Three stages of the filtration process

Before you decide on what filter you want to use, it is important to have a basic understanding of how the filtration works! These are the three types of filtration that should be taking place with a brief explanation of each.

Image Stage Filter media

Filter pad flossFilter pad floss

Mechanical sponge (foam), floss pad, pre-filter media

Fluval CarbonFluval Carbon

Chemical peat, activated carbon (charcoal), phosphate remover, ammonia remover…

Fluval Biomax ceramic ringsFluval Biomax ceramic rings

Biological ceramic rings, bio-sponge (foam), bio balls, Eheim substrat pro, coral bone stone…

1. Mechanical filtration

This is usually the fist stage of filtration. Mechanical filtration means physically removing debris and other floating dirt particles in order to keep water crystal clear.

Generally, filter media like filter wool or ceramic rings are used for mechanical filtration. Fine filter wools are used to catch fine particles whereas ceramic rings captures coarse particles before they clog up finer filter material.

By filtering out particulate matter mechanical filter media protect biological and chemical filter media from coarse debris and increase their life time. Mechanical filter media must regularly be rinsed or renewed in order to prevent clogging up.

2. Biological filtration

Biological filtration is the recycling of harmful chemical substances by bacteria. Fish waste such as urine, feces and respiration byproducts pollute water chemically with toxic substances such as ammonia. Ammonia is very poisonous to fish especially at high pH levels.

The recycling bacteria colonized on the surfaces of the biological filter media convert ammonia into much less toxic nitrate. This conversion – ammonia to nitrate – is called nitrogen cycle. If the aquarium is new it may take several weeks or even months before the bacteria reach a sufficient population.


Aquarium nitrogen cycle

Typically, porous filter media like ceramic rings are used for biological filtering due to their huge surface-area to volume ratio. Biological filter media should be rinsed with aquarium water in order not to harm recycling bacteria. Recycling bacteria colonize not only filter media but every possible surface in the aquarium such as gravel, rocks and plant leaves.

3. Chemical filtration

Activated carbon is commonly used as a chemical filter media in aquarium filters because it absorbs large molecules such as many organic substances and medicaments. This keeps the water clear and free of odors.

Peat as a chemical filter medium is widely used to reduce and stabilize pH (acidity) levels for keeping and breeding soft water species. To accomplish this job peat does not actually filter out or convert anything; it releases humic acids which increase acidity and reduce carbonate hardness.

Other commercial media like phosphate remover, ammonia remover,… may also count as chemical filter media as they remove harmful chemical substances from the water.

Most popular aquarium filter types these day

Once you have gotten past the decision of what type of filtration you want to use, there are several options and specs when looking at specific types of filters.

Below sections will help you to understand different types of filters available to you. There is a page for each type of filtration system (coming soon) that include more detailed descriptions that are linked within each filter category on this page.

Sponge (air driven filters)

This is the most simple of the aquarium filters and is commonly used in breeding tanks and while raising the fry. Occasionally this is an okay option for very small tanks if it is understocked and there are very small and delicate fish and/or invertebrates.

Air driven filters have some benefits for delicate situations but for most aquariums this is not the best choice for your main filtration system. They provide very limited filtration all around that are only suitable for very specific situations, though they do function well as supplemental biological filtration in addition to the use of a more advanced system.

Undergravel aquarium filters (air driven)

A step up from the sponge filters but still a very simple system. Like the sponge filters, chemical filtration is minimal if it is incorporated at all. The biological filtration and mechanical stages of filtration, however, are definitely an upgrade from the sponge filters.

Undergravel filters can provide adequate filtration by themselves in smaller aquariums that are very lightly stocked with fish. In most cases, undergravel filters will be much more beneficial in supplementing biological and mechanical filtration in any aquarium when used with more advanced systems.

Power filters / (HOB) Hang On Back filters

HOB filters are probably the most common filtration systems purchased by aquarists that are just starting out. They are not a bad option by any means, they hang right on the tanks rim with the bulk of the unit outside of the aquarium and they efficiently incorporate all three stages of filtration.

The fact that they hang on the back of the tank saves on space compared to an external canister filter (below.) These are typically rated for 75 gallon aquariums on the high end and in most cases I would recommend trying to avoid “maxing out” your filters recommended tank volume. (i.e. 75 gallon rated HOB = use for max 55-60 gallon aquarium)

It isn’t the very best option for filtration but it will get the job done and can absolutely be the only system used to filter your aquarium water.

Aquarium Power Filters Page –  In depth description, details, and product comparisons.

Internal aquarium filters

Internal filters are great if you really don’t have the space between the tank and a wall for a HOB filter nor the room to put an external canister. Of course, the filter has to go somewhere! If you are saving space outside of the aquarium, you are sacrificing space inside.

Is that a concession you are willing to make if you don’t need to? I know I’m not. These aquarium filter systems are fully equipped to handle your fish tank’s dirty water through the mechanical, chemical and biological stages and they can certainly do so efficiently.

Internal Aquarium Filters Page –  In depth description, details, and product comparisons.

External canister filters

This is quite possibly the best decision for filtering your aquarium. All of these systems are going to do a fantastic job filtering your aquarium water through all three stages.

Most external canister filter models are going to allow you to customize your filtration. There are many options for configuring your canisters filtration media to handle different mechanical, chemical, or biological filtration loads. It all just depends on the specific needs of your aquarium.

Aside from the ability to fine tune your filtration, external canisters simply do a better job of filtering the water in all three stages over any of the above mentioned types of aquarium filter systems.

If you buy a quality canister filter, you won’t need to replace it for a very long time, it will run quietly, and you will have continuously crystal clear water and consistent water parameters.

Canister Aquarium Filters Page – In depth description, details, and product comparisons.

How to choose right aquarium filters?


When you have settled on what type of filtration will work best for your ideal setup, the detailed pages that I just mentioned include comparisons of several brands, models, and sizes for each type of filter; All in hopes of helping you make the best choice for your unique freshwater aquarium!

Besides choosing a filter type you want, you will need to know how to choose a suitable filter for your aquarium. This depends on the size of your tank and species of fish it houses.

The thumb rule is to choose a filter that turns over four times of your aquarium water in an hour. For example, a 20 gallon aquarium will need a filter with a flow rate of around 80 gallons per hour (GPH)

A too weak filter can’t circulate your aquarium well that will end up the health problems of your fish. And vice versa, you can’t really over filter your aquarium.

Having a filter that is much to powerful for your aquariums size is only negative in the sense that the output flow from the filter will be too strong. This may cause stress and kill your fish, as well as destroy your beautiful aquascape that takes you a lot of time to fulfill.

All aquariums are very different which means that the best aquarium filter systems for your fish tanks will unlikely be the same as the best means of filtration for my fish tanks. Some fish love strong water flow while some like Bettas enjoy swimming slowing in a quiet environment. And your work is provide the right environment for your aquatic pets.

Getting the best quality filtration system for your aquarium can save you from a lot of future hardship. (ammonia spikes, sick or dead fish, easier maintenance…) And it’ll help keep the water looking crystal clear for much longer!

Getting the cheapest filters can cost you more money in the long run. (More frequent media changes, more frequent water changes, malfunctioning equipment, you upgrade down the road anyway…)

In The End

Filtration comes in a handful of different forms and there are a ton of brands, models, and varieties within the different aquarium filter systems. If your looking at a page full of filters and prices, it can be overwhelming.

But it doesn’t have to be overwhelming!

I will leave you with my 2 biggest pieces of advice regarding your decision.

First: Make sure that your filter incorporates the 3 types of filtration (Mechanical, Biological, and Chemical) efficiently enough for your setup. Primarily basing what is efficient enough on the volume of your tank.

Second: Equip yourself as best as you can, after all, aquarium filter systems are pretty much the backbone of your aquarium. Without filtration, you do not have an aquarium, you have a glass case of water with dead things in it!

You may like

Leave a Reply

Your email address will not be published. Required fields are marked *