Did you know that almost all types of aquariums require a filter in order to become a thriving mini ecosystem? Not only does the filter remove floating particles to make the water look nice and clean, but it also contains a large amount of the beneficial bacteria that make the all-important nitrogen cycle possible.
A quick trip to the aquarium store will reveal a dazzling range of different filter types. Which one should you pick? Let’s have a look at the most common types of aquarium filters to help you figure out which one will work best for you.
Tip: The filter is one of the most essential pieces of equipment in the aquarium. If you don’t know why your tank needs one or what the nitrogen cycle is, head over to the article on cycling an aquarium first to learn more about this crucial process and the role aquarium filters play in it!
Types of Aquarium Filters
Internal Filter: Ol’ Reliable
When it comes to aquarium filtration, the internal filter is the classic. Like other filters, it consists of a casing stuffed with sponges and other filter media, a water intake tube or slots, a pump to move water through the media, and a spout or nozzle to spray it back out.
As the name suggests, an internal filter goes inside the aquarium. This is why, despite the fact that they’re often the cheapest choice, some aquarists don’t like them: they feel that unless the tank has a hidden equipment compartment, an internal filter is unsightly and gets in the way. Still, they can be very handy!
Internal aquarium filters exist for all but the smallest nano aquariums and are mostly used for tanks up to 75-100 gallons. For larger water volumes or heavily stocked tanks, the internal filter’s limited capacity means that it’s often better to opt for a canister filter or even a sump instead (see below).
| Advantages | Cheap, easy to find, easy to run |
| Disadvantages | Takes up space, not for XL tanks |
Sponge Filter: The Shrimp Keeper’s BFF
Have an aquarium that doesn’t need much in the way of filtration? Or one that contains very fragile aquatic life, such as dwarf shrimp or baby fish? Most filter types produce relatively strong water flow, and their intakes may even suck up small creatures if you don’t cover them with mesh or sponge. Not ideal!
That’s why for the not-so-heavy-duty operations, most aquarists prefer sponge filters. These small devices don’t contain a regular pump, but are hooked up to an air pump instead. Air is pushed through the hollow center of the sponge filter, and as it bubbles up to the surface, it pulls water through the sponge.
Although sponge filters mostly provide mechanical (rather than biological) filtration and aren’t suitable for heavily stocked tanks, their very gentle, adjustable flow makes them a popular choice for grow-out tanks, low-bioload set-ups with mostly plants, or aquariums that contain delicate fish or invertebrates.
The largest sponge filters are rated for 40-50 gallons. Above that, you’ll have to consider one of the other options.
| Advantages | Gentle, cheap |
| Disadvantages | Air pump can be noisy, only for small tanks |
Hang On Back Filter: The Reliable All-Rounder
Want to save space inside your tank by not using internal filtration, but don’t mind still being able to see the filter? A hang on back (or HOB) system will sit on the rim of your aquarium, pull water in, and let it fall back into the display portion. It’s quite elegant!
Hang on back aquarium filters provide circulation and air exchange at the surface, while the inside of the filter has plenty of space for both mechanical and biological filtration material. In fact, some heaters also have a slim enough profile that they can be hidden in a large HOB filter, meaning you get even more room in your tank.
HOB filters are easy to run and clean. In fact, many of them allow you to simply remove the lid and take out filtration media for cleaning or replacement, without needing to stop the filter or take it apart. Newer HOB filters now also sometimes come with a protein skimmer built in, which is a handy feature for saltwater aquariums.
| Advantages | Cheap, saves space |
| Disadvantages | Not for XL tanks |
Canister Filter: The Heavy Lifter
An unobtrusive option favored by aquascapers and folks with larger (100+ gallon) tanks is the canister filter. As with an HOB filter, the only parts that sit inside the tank are the intake and the outflow. The filter canister itself is hidden, usually in the aquarium cabinet. You can even use transparent glass in and outflow pipes, making the whole device nearly invisible.
Canister filters can be very powerful, and they provide plenty of space for loads of biological filter material, which can really help keep the tank stable and your fish happy. Many even have a compartment for a heater.
Performing maintenance on a canister filter is a bit more hands-on. It has to be stopped and opened up for cleaning, but many aquarists find the learning curve more than worth it. If this is your first time running a canister, be sure to keep the manual on hand so you know how to close the tubes and pump out air if need be.
| Advantages | Excellent filtration, aesthetically pleasing, suitable for large tanks |
| Disadvantages | More expensive, has a learning curve |
Did you know? Many filters, particularly canisters, come with the option of using different outflow nozzles. For efficient oxygenation (very important!), you can choose a spray bar, while for a nice and gentle flow in a planted tank, many aquarists prefer glass lily pipes.
Built-in Filtration: The Stealth Filter
The availability of different all-in-one aquarium sets has changed the hobby for the better. Everything from the smallest picos to tanks as large as 50+ gallons is now available in a “plug-and-play” version with all equipment included.
An all-in-one tank may come with an internal filter, but our favorites have a built-in, hidden filtration compartment in the back of the tank. These include return pumps, and in some cases even a skimmer. The filtration section comes with multiple chambers where you can place your favorite filter media, or even make a section into a mini refugium with a submersible light to grow filtering macroalgae.
A media caddy allows you to use carbon, GFO for phosphate control, or other adsorption media like Purigen. Depending on the tank you buy, the hidden filtration section will likely accommodate a heater. It may even have enough space for a media reactor or protein skimmer!
Built-in aquarium filters make a great option for those who want more control and don’t like unsightly internal filters, but also don’t want to go for a big sump (see below).
| Advantages | Customizable, invisible, suitable for XS to XL tanks |
| Disadvantages | Has a learning curve |
Sumped Filtration: The Ultimate Powerhouse
Like the idea of a built-in filter, but have an aquarium that didn’t come with one? Or maybe you just want space for EVEN more equipment? Better filtration and squeaky-clean water? Take a look at sumped aquariums! Your display can be full of life and vibrant colors, while your equipment lives in a second tank, hidden by your aquarium cabinet behind closed doors.
Sumped tanks use an overflow to drain water out of your aquarium, while a return pump in the sump pushes it back up and into the display. While the water is moving through the sump, it flows through any equipment/filtration you decide to add. This can include a skimmer, reactor, bio media blocks, a refugium, and much more.
You can add your own sump to your tank with a HOB overflow if your tank doesn’t already come reef-ready (pre-drilled for plumbing). The extra water volume that a sump adds to your tank is beneficial for many reasons; the more water you’ve got, the easier it is to keep the parameters stable. Small mistakes will have less of an impact.
| Advantages | Highly customizable, invisible, suitable for XS to XL tanks |
| Disadvantages | Steeper learning curve |
Natural Filtration: The Balanced Ecosystem
If you’re looking for a tank that filters itself, and don’t want to stuff it to the gills with living inhabitants, consider natural filtration! This kind of aquarium relies on flow, oxygen, lots of plants or live rock (depending on whether the tank is freshwater or marine), and natural bacterial colonies to break down excess nutrients and waste. In freshwater tanks, natural filtration is sometimes referred to as the Walstad method.
You’re likely going to be making up for the lack of filtration by doing more water changes, but if that doesn’t scare you, then natural filtration can be a good fit!
A circulation pump and heater will keep your bacterial colonies thriving, while adding an air stone will give them plenty of oxygen to work with. Live plants or live rock help deal with excess nitrates and phosphates.
| Advantages | Cheap, learn about natural processes |
| Disadvantages | Only for lightly stocked tanks |
There are many aquarium filters to choose from, including some more uncommon types that we haven’t discussed here (see the DIY matten filter concept, for example). Which type you should choose depends on the type of aquarium you want to set up.
Keeping it simple is a good option if you don’t feel the need to have a lot of fish, while heavily stocked tanks might benefit from something like a sump. For most standard home tanks, internal, HOB, or canister filters work fine.
Dreaming of your own beautiful freshwater aquascape or saltwater reef, but don’t want to deal with things like having to choose the right kind of filter? We can help! The FantaSEA Aquariums team gets our hands wet so you don’t have to. Contact us with your ideas so we can design, build, and maintain your dream tank for you.
