A good aquarium must keep the water clean, and doing so requires adequate means to filter the water, remove pollutants and purify the water. Stay with us to find out all about how to choose the right filter system for your aquarium!

How to filter aquarium water?

Technically, there are three ways to filter aquarium water:

  • Biological filtration refers to the process by which beneficial bacteria break down ammonia and nitrite and transform them into compound nitrate, which is much less toxic. For beneficial bacteria to thrive, oxygen-rich water is needed, as well as a surface to which the bacteria can adhere, such as rocks or sand. All aquariums should have some provision for biological filtration, and with very small fish populations, this alone may be sufficient to keep the aquarium in good condition. However, in most aquaria, biological filtration will be just one method to be combined with others. So what is a biological filter? The biological filter (sometimes called a biofilter) in a fish tank is a cylindrical shaped filter connected by tubes that allow water to pass through. This filter serves as a home for bacteria that break down fish waste to keep the environment safe and non-toxic.
  • Chemical filtration is a process by which chemical additives remove dissolved waste from the water. The most common method for chemical filtration uses activated carbon.
  • Mechanical filtration is what most people think of as true filtration: machinery that removes solid particles from the water by circulating the water and filtering it through some type of aquarium filter. It is important to understand that mechanical filtration alone is not sufficient, as it does not remove or convert ammonia, nitrate or nitrite in the water. Mechanical filtration serves to remove free-floating debris before it breaks down into harmful substances and, to be beneficial, the filter material must be cleaned or replaced every two to four weeks. In addition to filtering pollutants from the water, mechanical filtration helps to move the water.

To maintain an aquarium effectively, a filter should pass all the water in the tank through the filter at least four times every hour. When choosing a system, pay attention to the type of filtration it offers: biological, chemical or mechanical. Some systems combine the different forms of filtration, with varying degrees of success.

Types of filter for your aquarium

There are 6 types of filtration systems to choose from:

Box or corner filters

Also called corner filters or internal filters, these were the first aquarium filters available for home aquariums. Although less common than in the past, they are very economical and can be loaded with a variety of filter media. Many box filters are compact units that attach to the glass inside an aquarium, making them suitable for small aquariums.

Some types require an air pump and air line to produce the necessary motion to move water through the filter. These systems create air bubbles that also enhance chemical and biological filtration.

Vessel filters

These are powerful mechanical aquarium filters that are best suited to medium to large sized tanks. Because canister filters are placed outside the tank, they can easily be hidden behind or under the aquarium stand. These large units provide very good mechanical, chemical and biological filtration. Canister filters are pressurised to force water through the filter media, rather than allowing it to flow through as other filters do.

Diatomic filters

Diatomic systems are specialised aquarium filters that “polish” the water by removing very small particles. In design, they are similar to diatomaceous earth pool filters, which work by pumping water through a layer of very fine particles to clean the water.

Diatomic filters are most often used in temporary situations when fine particles, such as diatomic algae, are a problem. Because a diatomic filter is used only for special situations, some standard filters are manufactured with diatomic inserts so that they can perform a dual function when necessary.

Sponge filters

The sponge filter is placed over a tube of a power head or air pump. As water is forced through it, bacteria will grow and establish biological filtration. Sponge filters also provide mechanical filtration, although they clog quickly if there is excess debris. They are excellent for tanks with very young fish, as the sponge prevents the fish from being sucked through the pump.

Trickling filters

Also called wet/dry filters, trickling filters are designed to expose the water to as much air as possible. This is accomplished by allowing the aquarium water to drip into a container with media such as plastic balls, strands or dental floss. This exposure to air and water encourages large colonies of beneficial bacteria that break down waste. These are especially popular for saltwater tanks, but are also becoming increasingly popular in freshwater aquaria. Chemical filtration is provided by placing chemical media in the filter.

The major drawback is the fact that they clog quite easily, but the use of a mechanical pre-filter eliminates or reduces that problem.

Do you know of any other types of filters that are good to install in aquariums? Leave us your recommendations in the comments!