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Aquarium Filtration Systems

aquarium filters

Maintaining a successful aquarium comes down to a few key core components with one of the most vital being water quality. An aquarium filter is the life support system making the water safe for your finny friends by neutralizing or removing debris and impurities from the water. 

There are numerous filter systems to choose from, each with their strengths and weaknesses. When trying to decide on the right filter for your aquarium you need to determine if the filter meets the mechanical, chemical, and biological filtration needs of your aquarium. As a general rule, the filter should turn over the total aquarium water 3 to 5 times every hour.

As implied the mechanical filtration portion is responsible for removing debris and particulates from the aquarium water. This typically takes place by pushing or pulling water through some type of fiber or foam material, separating the debris from the water. 

The chemical portion of the filter utilizes some type of media, like activated carbon, to attract and adsorbs organics chemicals and compounds from the water. 

Last but not least, one of the most important of the filtration processes is biological. Beneficial bacteria are responsible for breaking down toxic ammonia and nitrite into less toxic nitrate, making the water safe for your finny friends. Beneficial bacteria will grow on most surface areas in the aquarium but is best to offer an area, like a power filter, that will not be disturbed and provide an oxygen rich environment. 

Types of aquarium filters

There are a lot of different filters available, so let’s explore some of the pros and cons of the more popular ones. 

Sponge filter

Not just for cleaning, a sponge filter is just as the name implies. Sponge filters utilize an air pump or a powerhead to draw water through a foam sponge, trapping detritus and debris from the aquarium. The sponge offers a large surface area for beneficial bacteria to grow, making it a great biological filter. Sponge filters are great for smaller sized aquariums and utilized by fish breeders as they offer a gentle flow and do not pose harm to small fry like a power filter might. Because of their simplicity, they are also a good option for quarantine tanks. 

A few drawbacks, sponge filters do not contain a chemical filtration component. They can be a little trickier to clean since you are unable to just rinse and clean these in the sink as that would kill off the beneficial bacteria. Sponge filters are best suited for smaller aquariums or ones containing low bio loads. 

Recommended sponge filter

Box filter

The great grandfather and the first to the scene for home aquariums. Box, also known as corner filters, work similar to sponge filters. These are typically a plastic box that is operated with an air pump and air stone. Just like the sponge filter they are great for smaller, breeding or hospital tanks. The benefit of a corner filter over a sponge filter is the ability add various types of filter media, giving the benefit of the chemical filtration. Most are compact in design which will limit their ability to filter larger volumes of water. 

Undergravel filter

Definitely not the new kid on the block, under gravel filters were the mainstream filter for years of aquarium keeping. Depending on the size of the aquarium, this filter consists of a single or multiple perforated plates that sits on the bottom of the aquarium, covered by substrate. A single or multiple tubes are connected to the plate and run by an air pump and air stone, or a powerhead. This draws water down through the substrate trapping debris and creating a large surface area for beneficial bacteria. Some offer carbon attachments, providing some chemical filtration. 

A few cons with this type of filter, substrate needs to be adequate sizing. If too small this can block and plug the slits in the plate. If too large it will not trap the detritus appropriately. Detritus can build up over time causing increases in dead spots and nitrates. Beneficial bacteria require oxygen, this filter design can limit dissolved oxygen levels at the bottom of the tank thus limiting bacteria populations. Using a powerhead to operate it omits the chemical filtration option.

Recommended undergravel filters

External and internal power filters 

The mainstream filters of today, power (aka, hang on the back) and internal power filters offers efficient and effective filtration. Power filters provide great biological, mechanical, and chemical filtration in a simple to operate unit. Internal power filters are smaller versions of hang on the back versions and great for smaller sized aquariums.  These filters operate with an electrically driven motor and impeller which draw in large volumes of water. They are simple to operate and maintain, generally only requiring a monthly change of a filter pad housing activated carbon and the occasional deep cleaning of filter box and impeller. There are numerous variations and designs offered, with some containing a bio-wheel for added biological filtration, providing options for most aquarists’ needs. 

These filters can be more expensive than some of the other options listed above, but are well worth it. Because they are mechanical there is a risk of component failure. Another drawback is  that hang on the back filters stick out from the back of the aquarium preventing the tank from being tight against the wall. 

Recommended external and internal power filters

Canister filter 

Canister filters are kind of like the best of all the filters rolled into one. Similar to the function of hang on the back filters, most canister filters have large compartments that hold a large volume of filter media making them a great option for larger aquariums. One benefit in their design is the water is channeled and forced through the media chambers, improving the filtration of the water. Another plus is they sit outside the aquarium and are connected via hoses- this allows the filter to be hidden or placed in base of the aquarium stand. Like the power filters, there are several options available. 

On the downside, they fall into the higher end of the price range when compared to most other filters. Because of their design, canister filters can be a little cumbersome to maintain from cleaning to media replacement when compared to other filter types. 

Recommended canister filters

Fluidized Bed Filters

Fluidized bed filters (aka, sand filter) are designed to be biological power houses. These filters use a sand, plastic, or silica chip media in a tube or box type chamber to grow beneficial bacteria. Utilizing a water pump, the aquarium water is pushed from the bottom of the chamber causing the media to float or become fluidized. This filter is primarily focused on the biological form of filtration, but it will perform slight mechanical filtration by trapping some debris. There is little maintenance required for these filters, but the pump will need to be maintained. 

Some negatives, if this is a hang on the back design it will prevent the aquarium from being placed tight against the wall. There is also no chemical filtration provided and they do not provide a ton of mechanical filtration so it would be best to prefilter the water prior to entering the canister filter. Finally, if the power goes out the sand can become compacted and may be difficult to get restarted. 

Wet Dry Filter

Wet dry filters (aka, trickle filters) have been widely utilized by marine aquarists for years and have gained in popularity for large aquariums. The popularity is driven due to their ability to filter large volumes of water, skim the surface of the water and house most of the tank equipment outside of the aquarium. Wet dry filters use a large compartment that houses a bio filter media, like bio balls which water trickles over via a drip tray or spray bar. This design provides a large surface area, maximizing air and water exposure. This allows for the water to become saturated with oxygen, assisting with the growth of large beneficial bacteria colonies. For the marine aquarium, these filters typically provide an area to house a protein skimmer to aid in filtration. 

A few drawbacks with this type of filter verses others are they can be more costly than other forms of filtration. They are larger, potentially taking up more space and require a larger area within the aquarium stand to be placed. If the water is not prefiltered the bio media can become clogged by detritus, reducing the effectiveness of bio filter and increased nitrates. 

Algae scrubber 

No, this is not the same as an algae scrubbing pad! This was a filter developed back in the 1970’s that utilized the natural abilities of algae to “scrub” nutrients and carbon dioxide from the water. There are a couple different versions of this filter, but this filter uses a box or plate exposed to strong lighting allowing the algae to grow in a manageable area. The water is drawn through or run over the algae, providing it the nutrients it requires to grow. 

Algae scrubbers are not as common as other filtration types and can be costly devices to purchase. The major con with this type of filters is that if something fails with the lighting, there is potential for the algae to die off, making the filter ineffective.  

Diatom filter 

Not as common now a days, diatom aquarium filters were once popular for keeping the aquarium water crystal clear. They primarily only offer the the mechanical form of aquarium water filtration. Diatom filters are designed to utilize very fine diatomaceous earth powder. This is placed into the filter to create very small pores in the filtration bag to trap the smallest of particles in the water. These filters are great for removing free floating algae responsible for creating green water. 

Now for the drawbacks… There are very limited manufacturers making them a little harder to find. They do not offer any chemical or biological forms of filtration and the filter media can become exhausted quickly, requiring a little more maintenance than other types of filters. 

Which filter is right for you?

So, which filter is right for you? Our best recommendation is to do your research to identify which type checks the most boxes for your aquarium’s specific needs. Whether you are looking for your first aquarium filter or upgrading from your current one, there are many options to choose from so please stop into your neighborhood pet care center and discuss your aquatic needs further with one of our many knowledgeable aquatic specialists.  

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Reviewed by Don Spaeth, Petco’s National Aquatic Care, Education and Programs Manager

Don is Petco’s National Aquatic Care, Education and Programs Manager. He is an avid aquarist who has worked with and cared for freshwater and marine aquatic life for over 40 years. Throughout his 27+ years with Petco, Don has actively been involved with our aquatic vendor partners and worked to promote aquatic education both in store and company-wide.