Fish Tank Filters: Which One Should You Get?

What is the most common reaction of people to hear that you keep fish for pets? 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. You may find some filters more effective than others. Here is a quick overview of each category.

Mechanical Filtration uses filter socks, sponges, and filter floss pads to remove debris from water. It is much like 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 filters use activated carbon or other special resins to remove any medications, tannins, or other impurities. 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.

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 loved 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 Fillter

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, and airline tubing that connects them. Air is pushed through the tubing and into the sponge filter’s hollow cavity by the air pump. The sponge walls draw water through the rising bubbles of the air, which mechanically collects any debris and gives place for beneficial bacteria to grow.

Cons: I could keep going, but this device has few mechanical parts, so it is very affordable, easy to clean and hard to break. It allows for good water circulation and surface stirring, and is gentle enough not to eat shrimp or fish fry. 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.

The bottom line: Sponge filter are a common item in fish shops, fish rooms and breeding facilities. They’re reliable and economical. Why not use what’s tried and true?

Hanging-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.

Advantages: What I love about filter media is how customizable it can be and that you can add 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. The AquaClear filter that I have has a variable flow rate. This allows me to adjust the water circulation according to my needs.

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. 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 have extra features such as an automatic priming, UV sterilizer, inline heater and UV sterilizer. Many hobbyists consider it to be one of the best readymade filters on the market.

The cons: Performance is not free, and this can make it a bit expensive. 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. Be prepared to spend more money and take longer to purchase this premium product.

Fluidized Bed Filter

Ziss moving filter, powered with 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. 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 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. The noise level is comparable to that of a sponge filter, mainly due to the bubbles and pump.

The bottom line: A fluidized bed filter is a great way to improve your biological filtration. 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 every aquarist always wants to know. First, I haven’t covered all the 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. Consider the needs of your aquarium – such as your stocking levels, water circulation, ease of use, and budget – and pick the solution that works for you. Happy filter shopping and good luck!