Every aquarium needs a filter- it seems to be pretty common knowledge.
But beyond that the confusion starts.
One glance at the options available at the local pet store or online retailer can leave the beginning aquarist lost in a sea of possibilities.
And the manufacturers tend to not make it any easier.
No matter what type or size of filter they're selling it's the right one for you as far as they're concerned.
This leaves it up to you to pick the best option for your aquarium setup yourself.
To do so, you're going to need a bit of knowledge both of what it is an aquarium filter actually does and how the different options available accomplish this.
First, a bit on the three main types of filtration and why each is important.
Every filter will fill at least one of these roles and some may fill all three.
Mechanical Filtration Mechanical filtration is the simplest and easiest form of filtration to understand.
Basically, mechanical filtration means passing the dirty water through some sort of media that will physically trap any free particulate it carries.
In a typical aquarium setting think of filter pads or sponges.
Mechanical filtration's job is to capture these relatively large bits of waste so they can easily be removed from the system either by washing or changing the filter media before they have a chance to break down further.
Chemical Filtration Not all the waste in your aquarium is in a solid form that can easily be extracted through mechanical filtration.
The goal of chemical filtration is to remove waste products that have dissolved into the water by absorbing them into some type of media.
In aquarium filtration the most common method is to use activated carbon.
Activated carbon is able to trap many different common waste products associated with aquariums.
Various other chemical filtration medias also exist, many of which target specific pollutants.
Biological Filtration Biological filtration is vary similar to chemical filtration but instead of using a reactive media bacteria do all the work.
Commonly known as the nitrogen cycle, every aquarium, whether the owner knows it or not, depends on bacterial colonies to keep the water habitable for its occupants.
These bacteria break down the waste products produced by fish and convert them to less harmful substances.
And while these bacteria aren't particularly picky about where they live (they'll eventually colonize more or less every surface within the tank) specialty filters and media have been created to give them an ideal environment to thrive and do their work.
Meeting the biological filtration needs of your aquarium setup is absolutely necessary for success.
And while the beneficial bacteria will grow throughout your tank giving them a dedicated place to colonize with ideal conditions will greatly improve their effectiveness.
Mechanical filtration is also quite important, if only to reduce the amount of upkeep your aquarium requires.
Chemical filtration is the least important.
It can help polish the water til it's crystal clear or prolong the time between water changes but it isn't absolutely necessary.
Still, having a filter where chemical media can be utilized should the need arise is a nice option to have.
So what are your options? Well, plentiful would be one way to put it.
All sorts of methods of filtration have been devised over the years making it easy to find a filter that's just right for any potential aquarium setup.
Let's take a look.
Undergravel Filter (biological/mechanical) This is a very old technique and not really employed much anymore but some people still swear by them.
As the name suggests the bulk of this filter is located under the gravel in the aquarium.
It consists of a molded piece of plastic that when placed under the substrate creates a thin empty chamber covering most of the bottom of the tank.
The plastic is perforated with lots of holes and so is basically like a mesh.
It also has a few larger holes to connect riser tubes that stick up out of the substrate.
A pump is hooked up to these tubes to pull water through them which in turn pulls water down through the gravel.
The idea is that the gravel can function as a media for bacterial growth as well as mechanical separation as waste is trapped within it.
Undergravel filters can be very effective but they require proper maintenance to maintain.
They can become easily clogged if not kept clean with frequent vacuuming.
Fine substrates and/or fish that like to dig don't mix well with undergravel filters either.
Sponge or Box Filter (biological/mechanical/chemical) A sponge filter is about as simple as it gets.
It's just a sponge that water is pumped though, either with a powerhead or with an air pump (the rising bubbles create a mild current that draws water though the sponge).
This works as a mechanical filter trapping waste as well as providing lots of surface area for biological filtration to occur.
A box filter is essentially the same thing, but instead of a sponge it consists of a perforated plastic box filled with filter floss and sometimes carbon to offer some chemical filtration ability as well.
Sponge filters are great for situations where strong currents could be problematic such as a fry tank.
They are also very easy to maintain- it's as easy as giving the sponge a quick rinse when it starts to get gunked up.
The drawback is that they are a bit unsightly since they're essentially just a big sponge that sits in the tank.
Hang On Back (HOB) Filter (biological/mechanical/chemical) A Hang on back, or HOB, filter is just what it sounds like- a filter that hangs on the back of the aquarium.
It consists of a chamber for holding filter media that is connected to the tank via a piece of tubing with a pump on the end to pull water into the filter.
Once the water has passed through the media is flows over the edge of the chamber and back into the tank.
HOB filters are very popular for small to medium sized tanks and are readily available in all manner of different sizes and configurations.
Some of them can also be configured to hold varying types of media but even the simplest ones offer all three types of filtration.
Overall HOB filters are very simple and easy to set up and maintain.
Canister Filter (biological/mechanical/chemical) Like with all the other filter types the name canister filter is pretty descriptive of what it is- a sealed canister filled with filter media and connected to the tank via some tubing.
Canister filters typically have some sort of basket or tray system for organizing the filter media and can be loaded with whatever you choose as you see fit.
They're capable of holding much more media than other filters and since the canister is sealed the water is forced to pass through it all instead of going around as it can in other designs.
This makes them a great choice for larger systems.
They're also a good choice if you would like to place the filter either in the aquarium stand or in some other out of the way location since the tubing it connects to the tank with allows you some freedom in this regard.
Wet/Dry or Trickle Filter (biological) The bacteria that drive the biological filter process need two things: their preferred food (either ammonia or nitrite) and oxygen.
A wet/dry filter attempts to maximize the amount of oxygen available to the bacteria by raising the filter media out of the water.
Of course if the media drys out completely the bacteria will die, so water is continually poured over the media to trickle down and keep it moist.
The media is usually either a rough shredded plastic or molded plastic balls with a mesh-like surface.
Both are designed to maximize the surface area available to the bacteria.
Wet/dry filters most commonly are implemented as part of a sump, though a few companies produce HOB type designs as well.
Protein Skimmer (mechanical) When considering setting up a marine aquarium quite often you will see a protein skimmer recommended.
A protein skimmer is essentially a type of filter that uses air bubbles to separate waste from the water.
The basic design of every protein skimmer is a vertical tube that water is pumped through.
Fine air bubbles are introduced which form a foam.
The foam gathers at the top of the tube and eventually spills out into a collection cup.
Protein skimmers are a highly efficient way to remove much of the waste from the water before it has a chance to break down.
Unfortunately for freshwater hobbyists they only work with saltwater.
Refugium (biological) Much like the protein skimmer, a refugium is something you might see mentioned if you're planning a saltwater setup.
A refugium is basically a small secondary tank free from predators where all sorts of algae and planktonic creatures are allowed to grow and consume the wastes that would otherwise cause issues in the display tank.
In addition to keeping the water clean, a refugium can supply the tank with a steady stream of microorganisms that your fish and corals love to eat.
Typically a refugium is built by the aquarist by installing some baffles into a sump and adding a light.
However, purpose built units are increasingly becoming available.
Every aquarium needs filtration and truth be told there are lots of options that will get the job done.
Regardless of the type all filters perform the same basic functions in more or less the same ways.
A basic well maintained sponge filter can keep the water just as clean as a pricy canister filter.
What it usually comes down to is your personal preference and finding a filter that fits into your aquarium setup well.
Whether it be easy maintenance or lots of flexibility there is a filter to suit your needs.