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? Most people think back to their great aunt’s goldfish tank that was covered in mystery slime and smelled of stagnant 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. Some filters work better than others. Here’s an overview:

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 works as a garbage container that collects trash. As such, you, as the fish owner must still clean the filter media. – 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. Once the chemical filtration becomes saturated with impurities, the media is no longer able to absorb pollutants from the water

Filter media can be classified as either biological, chemical, or mechanical.

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

The most basic filter requires at least three components. A sponge filter, which sits inside the tank, an air pump (which is outside the tank), as well as airline tubing to link them. The air pump pushes air through the tubing into the hollow cavity inside the sponge filter. The sponge walls pull water through the tubing, allowing the bubbles to draw in water.

Advantages: There are many pros to this device. It is easy to use, cheap, and durable. It allows for good water circulation and surface stirring, but is gentle enough not to eat shrimp or fish fry. 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. You can’t add chemical filtration to the sponge filter. I personally don’t like the bubbling sound from a sponge filter, but that’s easily remedied with a little air stone.

Bottom Line: Sponge filters are frequently found in fish stores, fish rooms, and breeding facilities because they’re so reliable and cost-effective. Why not use what’s tried and true?

Hang On-Back Filter

Hanging-on-back filter to 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. A hang-on-back filter performs better than a sponge filter at mechanical filtration. You can also add a fine filter pad for extra polishing. 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. AquaClear filters have adjustable flow rates, which allows me to control the water circulation.

Cons Additionally, if you don’t like the waterfall sound, just raise the water level in your aquarium and you’ll barely notice the noise.

Bottom Line: This is the first filter I ever purchased and it’s still in use today for good reason. 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 even come with extras such as an inline heater, UV sterilizer and automatic priming. This filter is considered to be one the most powerful and quiet on the market.

The cons: Performance is not free, and this can make it a bit expensive. Also, that nifty little canister is pretty difficult to service, requiring you to practically disassemble the whole setup every time you want to clean out 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. The media swirls around like fluid when water flows through a chamber made of small media granules, such as sand or pellets. Because the media is constantly in contact with oxygenated waters, this constant churning greatly boosts bacteria growth.

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. The filter comes with a sponge bottom prefilter that prevents fry getting trapped and is easy to take out for cleaning. 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). Like the sponge filter, it’s not as customizable for adding chemical filtration or more mechanical filtration. And I’d say the noise level is also comparable to a sponge filter (mostly coming from the bubbles and air pump itself).

Summary: To improve biological filtration, a fluidized-bed filter may be a good option. 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 choose?

Ah, the one question every aquarist is always looking for. First, I haven’t covered all the 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!