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? 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. 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 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. The media can no longer absorb pollutants from water once the chemical filtration has become saturated with impurities.

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

The bottom line: mechanical water filtration clears your water, while biological water filtration keeps your water safe. Chemical filtration is best used to remove impurities from your 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 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. 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.

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. To prepare for an emergency, you can buy battery-operated pumps that will pump air to the sponge during power outages.

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. There is no way to add chemical filtering if you need it. Personally, I don’t like the bubbling sound of a sponge filter. However, this can be easily fixed with some air stones.

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

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.

The pros: I love the flexibility of the filter media and the ability to include all three types. 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. 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. 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. 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. 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. You will need to be willing to invest the time and money to get this premium product.

Fluidized Bed Filter

Ziss moving filter, powered with 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. Because the media is constantly in contact with oxygenated waters, this constant churning greatly boosts 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. 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). 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.

Summary: To improve biological filtration, a fluidized-bed filter may be a good option. One Ziss Bubble Bio filter holds 20-40 gallons water. It can be used alone or with another filter.

Live Aquarium Plants

Which filter should I choose?

Ah, the golden question every aquarist always wants to know. First off, there are plenty of other filters that I didn’t cover (e.g., 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. 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!