Dec 20

Guide to aquarium filters

Your guide to aquarium filter types: what kind of filtration is best and why

different types of filter

Aquarium filter types: canister, power, sponge, internal filters


Without a doubt, aquarium filters represent one of the most important elements of a properly functioning fish tank. Without proper filtration, your fish cannot possibly survive in the tank habitat you introduce them to.

The process of keeping the water clean and free of waste is so important that the aquarium industry has developed numerous solutions to approach the issue of filtration. A quick look at your local fish shop will show a wide variety of filters, each with their own advantages and disadvantages.

Understanding your aquarium filter types

Your aquarium water needs to be filtered in three ways to offer your fish a pleasant environment in which they can thrive. These three filtration methods are defined as follows:

• Mechanical Filtration. This refers to the physical act of pulling unwanted matter out of the water and leaving it in the filter, to be disposed of when you clean the filter. Dead plant leaves and foreign particles are commonly filtered mechanically. Vacuuming your tank regularly is also a form of mechanical filtration.

• Chemical Filtration. Chemical filters remove toxic chemicals by attracting them chemically to a filter medium as the water is pushed through them. Carbon is a very common filter medium for chemical filters because the majority of toxins will attach to carbon.

• Biological Filtration. Biological filtration takes place on the filter medium when beneficial bacteria consume poisonous waste products, saving your tank from becoming toxic.

What are the various aquarium filter types?

Since there are so many different filtration options available, beginning aquarists can easily feel overwhelmed by the number of different products available. The differences between these filters may seem quite complicated, but the following list of filter types described below will help make the subject much more accessible:

sponge filter

Typical air powered sponge filter

• Sponge Filters. The sponge filter is one of the most basic types available on the market. It is distinguished by its lack of complex mechanical, chemical, or biological components and makes an acceptable, inexpensive filtration solution for small tanks, hospital tanks, and spawning tanks.

The sponge filter operates by using an air pump to pull water through the sponge material where unwanted particles are caught and beneficial bacteria consume ammonia and nitrite. Despite its simplicity the sponge filter provides excellent biological filtration

• External Filters. External filters are very common for aquarium hobbyists because of their excellent combination of effective mechanical, chemical and biological filtration as well as their price. External filters are usually grouped into hanging filters (HOB) for medium-sized tanks and external canister filters for larger tanks.

Both of these filters draw water into a canister filled with filtering material that provide mechanical, chemical filtration and biological filtration.

Larger external canister filters also pressurize the water when inside the canister. Because the water is pressurized and there is no air-to-water contact occurring within the canister, biological filtration is not as effective.

• Internal Canister Filters. Aquarium filters that sit directly on the glass of the inside of your tank are called internal canister filters. These filters combine excellent mechanical, biological and chemical filtration with very quiet usage, being completely submerged.

The drawback to these types of filters is that they take up space inside the tank. If you are short on space or would like to keep your tank interior pristine and natural, you may want to look at other filters.

undergravel filter operation

Details of how an undergravel filter works

Undergravel Filters. These filters are installed underneath the gravel substrate of your tank and pull water through the gravel and into uplift tubes where it is again deposited into the tank. These filters use your gravel as a mechanical filter, but leave out the chemical element.

Undergravel filters are generally not recommended for a number of reasons: Biological filtration is limited to whatever bacteria live on your substrate, mechanical filtration continually builds up a mass of decaying matter under your gravel, chemical filtration is not present, and any plants you may keep will have to deal with having their nutrients siphoned off.

Chemical Filters. Aquarium filters that base their entire filtration process on chemical means often use activated carbon as their primary filter medium. There are other materials on the market, but carbon remains by far the most popular, and for good reason.

A chemical filter that uses activated carbon can remove a great deal of unwanted chemicals from your water simply by letting the water pass through the carbon. For this reason, many external and canister filters include a small chemical filter that uses carbon.

• Fluidised Bed Filters. Fluidised bed filters are cylindrical filters that hang off of the back of your fish tank. They connect to a water pump that forces water through the bed of small, heavy particles— often sand or silica chips.

These filters can be expensive, but they offer a very useful combination of mechanical and biological filtration while remaining generally low maintenance.

Many of these filters will provide successful levels of filtering according to their type, while sacrificing their efficiency towards the other two filtering methods. In order to realise all three filtration methods for the best quality water, you will probably want to combine two filters.

The benefits of combining filters

While a great deal of aquarium filters promise effective mechanical, biological, and chemical filtration, many aquarists prefer to use two types of filters that only perform a single filtration task each. Combining filters can provide distinct benefits that even a large all-in-one canister filter cannot meet.

One benefit of combined filtering is that of redundancy— if one of your filters breaks down, you will still have some filtering going on through the other filter. Since these devices are so critical for the continued survival of your fish, it pays to keep a backup running.

Another benefit is that dedicated filters perform their jobs better than mixed ones. A single mechanical filter that does not provide chemical filtration has access to more water and space for its filtration job than it would if it had to do double duty. For this reason, many aquarists prefer to purchase multiple dedicated aquarium filters.

Choosing aquarium filter media

So far, this article has covered the various types of aquarium filters available on the market and categorized them by the way they function. There is another important way to categorize these devices, however, and it is by the medium that they use to filter water.

Mechanical filters have the widest range of filter media options, generally categorized by the size of the particles they can capture:

• Fluval Prefilter Media. Essentially a coarse, sponge-like material, this is called prefilter media because it is designed to catch large debris before it makes its way to a finer mechanical filter.

• Filter Pads & Foam. This medium-grade sponge material will clean most visible debris from your water without issue, and do not need to be replaced as often as finer filter media.

• Filter Floss. This fine material requires higher maintenance in the form of more frequent cleaning, but leaves your water much cleaner in the process.

• Micron Filter Pads. The very finest filter media available, these pads can filter material that is only fractions of the width of a human hair in length. These filters require frequent replacement, but can make your water crystal clear and even parasite free in the process.

Other considerations for aquarium filters: noise

The filter you choose could make a big difference not just for the lives of your fish, but yours as well: certain filters will produce different levels of noise. Controlling that noise can be difficult with certain types of filter.

Large external filters are usually the most common culprits of unwanted aquarium noise. Those that pressurize the aquarium water will often have to make some commotion in the process.

In general, any aquarium filters that rely on air pumps are usually quite noisy. High quality filters tend to be much quieter than their less expensive counterparts, and many self contained external filters are reasonably quiet.

The quietest filters are those where the main pump is fully submerged in the water such as the internal canister filter which can be almost silent.



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