Fish Tank Filters: Which One Should You Get?

What is the first thing people think of when they hear that you keep fish as pets? They probably conjure up memories of their great aunt’s dirty goldfish tank, covered in mystery slime and reeking of stagnant swamp water. But you and I know the secret to having a beautiful aquarium with crystal clear water… clearly, we just need to find the perfect fish tank filter!

Why do Aquariums Need Filtration?

As one of the key components of an aquarium, filtration is responsible for moving and cleaning the tank water, making it safe for fish to live in. There are three types of filtration: chemical, biological, or mechanical. Certain filters are better at one type versus another, so here’s a brief overview of each category:

Mechanical filtering uses sponges and filter socks. Filter floss pads are used to physically strain out any debris in the water. This is similar to a coffee filter. Mechanical filtration acts as a garbage can that collects trash – which means you as the fish owner are still responsible for cleaning the filter media (in other words, “emptying” the trash can before it overflows). – Biological filtration uses beneficial bacteria or aquarium plants that can consume the toxic ammonia and nitrogen compounds that result from your fish’s waste. Beneficial bacteria grows on any surface, including the walls and gravel in your aquarium, so many filters come with biomedia or bio-rings with high surface area to provide more places for the bacteria to live. – Chemical filter uses activated charcoal or special resins to remove drugs, tannins and other impurities. After the media has been saturated with impurities, chemical filtration is no longer able absorb any pollutants from the water.

There are many types of filter media: biological, mechanical and chemical.

Bottom Line: mechanical filtration makes your water clearer, biological filtration makes your water safer, and chemical filtration is something best saved for removing impurities from the water.

What are the Most Popular Types Of Filters?

Now that you’re familiar with what filtration does for an aquarium, let’s talk about the actual equipment you can purchase (in rough order of most to least common).

Sponge filter

Aquarium Co-Op sponge filters

This filter is the most basic. It requires at minimum three components: a sponge filtre (which sits within the tank), an air pump (which sits out of the tank), and airline tubing that connects them. The sponge filter is hollowed by air pumps that push air through the tubing. The sponge walls pull water through the tubing, allowing the bubbles to draw in water.

The pros: This device is inexpensive, easy-to-clean, and difficult to break because it has few mechanical parts. It is gentle enough to not eat fish fry, shrimps, or other slow-moving animals, but provides water circulation and surface movement. Plus, during power outages, the beneficial bacteria on the sponge stays in the oxygenated tank water (which gives it a longer chance of surviving), and you can even purchase battery-operated air pumps to prepare for emergencies.

Cons: The sponge filter takes up physical space in the fish tank, so you may want to hide it behind a rock, plants, or other aquarium decor. Also, there’s no way to add chemical filtration if needed. I personally don’t like the bubbling sound from a sponge filter, but that’s easily remedied with a little air stone.

Summary: Spongefilters are often found in fish shops, fish room, and breeding areas because they are so reliable and affordable. Use what’s proven to work.

Hang On-Back Filter

Hang on-back filter for nano-tanks

Just as the name describes, a hang-on-back filter sits on the top rim of an aquarium with the filter box hanging outside the tank and the intake tube lowered into the tank. Water is sucked up the intake tube via the filter’s motor, passed through all the media in the filter box, and then typically returned back into the aquarium like a mini waterfall.

Pros: I love how customizable the filter media is and the fact you can include all three types of filtration. In fact, I’d say a hang-on-back filter is even better at mechanical filtration than a sponge filter because you can add a fine filter pad to really polish the water. The device is very simple to service since most of the media is outside of the aquarium, allowing you to easily remove the media for gentle washing. Plus, the AquaClear filter I own has an adjustable flow rate, so I can really crank up or slow down the water circulation as needed.

Cons: Because a power motor drives the water flow, there’s a chance it can burn out if the filter runs dry or accidentally sucks up sand (use a pre filter sponge to prevent the latter). Additionally, if you don’t like the waterfall sound, just raise the water level in your aquarium and you’ll barely notice the noise.

The bottom line: This was the first filter that I bought and is still in use today. As a popular staple in the freshwater aquarium hobby, the hang-on-back filter excels in all three arenas of filtration and has extremely flexible options for hot-rodding it to your tastes.

Canister filter

A canister filter is essentially filtration in a plastic cylinder or box form factor that often sits under the tank, with intake and output hoses that reach into the aquarium. A motor pulls water into the canister. The water then travels through several filter media trays and is returned to fish tank.

Pros: Just like the hang-on-back filter, the canister filter takes up very little room inside the aquarium and is highly customizable. Some models include extra features such as an inline heating, UV sterilizer, or automatic priming. As one of the most powerful and quiet options on the market, many hobbyists consider this to be the king of all readymade filters.

The cons: Performance is not free, and this can make it a bit expensive. It is also very difficult to service this tiny canister. You will need to disassemble it every time you want to clean the insides. Note: There is a greater risk of flooding during maintenance. Keep those towels handy! Finally, because the filter media lives outside the aquarium in a closed box, there’s a greater risk of suffocating and killing off your beneficial bacteria during a power outage.

Summary: If your discus needs extremely clean water or you have an African cichlid aquarium with high bioloads, then this might be the right product for you. Just be prepared to spend the extra money and time it takes to own this premium product.

Fluidized Bed Filter

Ziss moving bed filter, powered by an air pump

Fluidized bed filters were traditionally used for DIY filtration. But, now, there is a smaller, ready-to-use version called the Ziss Bubble Moving Media filter. Water flows into a chamber with small media granules like sand and plastic pellets. The media then swirls around as fluid. This constant churning greatly enhances bacteria growth from the media’s constant contact with oxygenated water.

Comments: The Ziss Filter is air-driven just like the sponge filter. This means that it has very few mechanical parts and can provide a lot more surface agitation to increase gas exchange. It comes with a sponge prefilter at the bottom that prevents fry from getting sucked up and is easy to remove for maintenance. As a device focused on biological filtration, it’s great for goldfish and turtle aquariums with high bioloads – and unlike sponge filters, the hard plastic is too hard for turtles to chomp through!

Cons: This filter is relatively tall at 11 inches, so it’s only suitable for taller tanks (not a 10 gallon or 20 gallon long aquarium). The sponge filter is similar in that it can’t be customized for chemical filtration and/or mechanical filtration. It is noisy, but not as loud as a sponge filter. This is mainly because of the air pump and bubbles.

Bottom Line: If you’re looking to boost your biological filtration, consider a fluidized bed filter. One Ziss Bubble Bio filter handles about 20 to 40 gallons of water and can be used either by itself or in conjunction with another filter.

Live Aquarium Plants

Which Filter Should I Get?

Ah, the golden question that every aquarist wants to know. First off, there are plenty of other filters that I didn’t cover (e.g., internal filters, sumps, and undergravel filters). There is no one “best” filter. Instead, there are many tools that can be used to accomplish different tasks. Take into account the needs of your aquarium (such as stocking levels, water circulation and budget) and choose the right solution. Happy filter shopping and good luck!