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. There are some filters that work better than others, so let’s take a look at each type.

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 filtration uses activated carbon or special resins that can remove medications, tannins, and other impurities from the water. After the media has been saturated with impurities, chemical filtration is no longer able absorb any pollutants from the water.

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

Summary: Mechanical filtration makes water clearer, biological filter makes water more safe, and chemical filtration can be used to remove impurities.

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 most basic of all filters requires at least three components: a sponge filter (which sits inside the tank), air pump (which sits outside the tank), and airline tubing to connect them. The air pump pushes air through the tubing into the hollow cavity inside the sponge filter. The rising bubbles of air draw water through the sponge walls, thus mechanically collecting debris from the water and giving beneficial bacteria place to grow.

Pros: I could go on and on, but this device is cheap, easy to clean, and hard to break since it has very 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. You can also buy battery-operated air pumps for emergency situations.

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. It’s best to stick with what is proven reliable.

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.

The pros: I love the flexibility of the filter media and the ability to include all three types. 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 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. With the aid of a motor, water is drawn into the canister, travels through several trays of filter media, and then is returned to the 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.

Cons: You have to pay for performance, and the price tag on this one can be a little steep. This handy little canister is difficult to service. It requires you to literally disassemble the entire setup each time you need to clean it out. 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. You will need to be willing to invest the time and money to get this premium product.

Fluidized Bed Filter

Ziss moving bed filter, powered by an air pump

Traditionally, fluidized bed filters have been more of a DIY approach to filtration, but now there’s a compact, off-the-shelf version known as the Ziss Bubble Moving Media Filter. Water flows into a chamber of small media granules (like sand or plastic pellets), causing the media to swirl about like a fluid. The media’s constant contact of oxygenated water greatly increases bacteria growth.

Advantages: Because the Ziss filter works in the same way as a sponge filter but is air-driven, it doesn’t have any mechanical parts to break. It also provides a lot of surface agitation which allows for greater gas exchange. It has a sponge prefilter on the bottom to prevent fry from being sucked up. This is also 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). It is not as easily customizable to add chemical filtration or mechanical filtration, like the sponge filter. The noise level is comparable to that of a sponge filter, mainly due to the bubbles and pump.

Summary: To improve biological filtration, a fluidized-bed filter may be a good option. A single Ziss Bubble Bio filter can handle 20-40 gallons of water. It can also be used in conjunction with other filters.

Live Aquarium Plants

Which filter should I choose?

Ah, the one question every aquarist is always looking for. There are many other filters I did not cover, such as internal filters, sumps and undergravel filters. Secondly, there’s no such thing as a one-size-fits-all “best” filter, but rather a wide variety of different tools that can best accomplish different tasks. You should consider the requirements of your aquarium, such as water circulation, stock levels, budget, and ease of use. Then, choose the best solution for you. Good luck and happy filter shopping!