Fish Tank Filters: Which One Should You Get?

What are people thinking when they hear that you have pet fish? People probably think of their great aunt who kept a dirty goldfish tank covered in mystery slime that smelled like 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. The three main types of filtration are mechanical, biological, and chemical filtration. 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 is like a trash can. You, the fish owner, are responsible for cleaning 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. After the media has been saturated with impurities, chemical filtration is no longer able absorb any pollutants from the water.

Examples of mechanical, biological, and chemical filter media

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 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 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 provides good water circulation and surface agitation, while being gentle enough to avoid sucking up fish fry, shrimp, and other slow-moving creatures. 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. The bubbling sound that a sponge filter makes is not something I like, but it can be fixed by using a little bit of 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.

Comments: I love that the filter media can be customized and you can use all three types of filters. Actually, a hang-on back filter does a better job at mechanical filtering than a sponge filter. It also allows you to add a fine filterpad to 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. 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.

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. The motor draws water into the canister. It then passes through several filters media trays before being returned to the 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.

Cons: You have to pay for performance, and the price tag on this one can be a little steep. It is also very difficult to service this tiny canister. You will need to disassemble it every time you want to clean the insides. Keep your towels handy as there is a higher chance of flooding during maintenance. 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

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.

Pros: The Ziss filter is air-driven like the sponge filter, so it has very few mechanical parts to break and provides plenty of surface agitation for increased 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). 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).

Bottom Line: If you’re looking to boost your biological filtration, consider a fluidized bed filter. 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

What filter should I get?

Ah, the golden question that every aquarist wants to know. There are many other filters I did not cover, such as internal filters, sumps and undergravel filters. Second, there is no “best” filter that fits all. There are many different tools that can accomplish different tasks. Take into account the needs of your aquarium (such as stocking levels, water circulation and budget) and choose the right solution. Have fun filter shopping!