Intro to Aquarium Filtration

The filtration system is arguably the most important component in an aquarium.  It is responsible for removing dangerous elements, particles and compounds from the water in order to keep your fish safe. However, filtration is complicated.  There are several types of filtration and several types of filters each with some positives and negatives.  This article will attempt to provide an overview of aquarium filtration by breaking down each piece into a simple, concise explanation.  We’ll also examine a few of the most common questions

Types of Filtration

Mechanical Filtration

Mechanical filtration is accomplished by pushing the water through a pervious sieve like material (typically some sort of sponge).  This will sieve out any larger particles that are in the water.  The particles are them be removed by cleaning the medium.

Chemical Filtration

Chemical filtration makes use of a chemical (typically activated carbon) to react with elements and compounds within the water to neutralize them.  The only issue here is that chemical filtration doesn’t only select the dangerous stuff and will also neutralize most antibiotics and medications.

Biological Filtration

Biological filtration relies on bacterial growth to eat fish byproducts and excrete less harmful byproducts.  There is typically a medium with a very high surface are (quite possibly that same sponge used in mechanical filtration) where bacterial grow and thrive.

Types of Filters

Air Driven Sponge Filters

Air driven sponge filters operate on sucking aquarium water through tubing that is covered in a sponge.  The sponge filters out any larger particles (mechanical filtration) and provides a perfect medium for bacteria to survive.  Air drive sponge filters are typically used on smaller volume aquariums and especially in smaller tanks used for breeding because they are low maintenance and can operate without substrates as required with undergravel filters.

Internal Filter

Dr. David Midgley [CCA-2.5]
Dr. David Midgley [CCA-2.5]
Internal filters are fully submerged filters which suck in water, pump it through the filter and then pump the water back out into the tank.  They often use suction cups to attach to the inside corner of the tank. These have the benefits of being very quiet.  They are most often used in aquariums where other filter types aren’t possible because of low water levels such as with frogs or turtles.

Undergravel Filters

Undergravel filters are located on the very bottom of the tank below the substrate.  The water is pulled through the gravel and then through the filter.  The water is then pumped up through a tube and then put back into the top of the aquarium water.  These filter are most common in smaller aquariums.

Power Filters

Сергій Мацапура - Youtube
Сергій Мацапура – Youtube

Power filters are the filter that hangs on the back of the aquarium.  A suction tube pulls water up into the water repository.  The repository is in a shape such that the water will overflow into the tank.  As the water moves from the back towards the tank, it moves through a filter medium that acts as a mechanical filter and provides a medium for beneficial bacterial growth.  The filter medium is also typically a bag in which activated carbon is located providing the chemical filtration.

Power filters are very common in mid sized tanks between 10 and 55 gallons.

Canister Filters

Pinpin [CCA-1.0]
Pinpin [CCA-1.0]
Canister filters are excellent for larger tanks that are heavily stocked.  They pump water out of the tank down into the canister which is typically sitting below the tank in the stand.  Within the canister, there are several layers (depending on the manufacturer) of filter media.  Canisters are larger than most other filter types which allows for a large amount of filtration and provides a very large area in which bacteria can live.  Once the water has been through the canister, it is pumped back into the aquarium. If you have a larger fish tank that is heavily stocked, canister filters are a great option.

Wet/Dry Filters

Wet/dry filters are typically used in large aquariums where biological filtration is the most critical aspect.  The filter is set up such that the biological filter medium is exposed both to the aquarium water and to the air which makes for optimal conditions for good bacteria.  They are a bit more complicated to set up than other filter types, but they can be worth the extra hassle.

Filter Sizing

As a rule of thumb, your aim should be to completely turn over the water 4 to 6 times per hour.  This means your filter should have a flow rate of 4 to 6 times your tank volume – filters are typically sized by gallons per hour (gph).  As your tank gets larger than about 100 gallons, this multiplier can drop down to 2 or 3.  Another factor to consider is whether your fish prefer a fast flowing water, such as the zebra danios  or a slower flow as the neon tetra.

Filters by Tank Size

If you have a tank smaller than 55 gallons, go with a power filter.  They are simple to install and maintain and they are very reasonably priced.  If you have a larger tank, a canister filter is typically the way to go.  If you have a smaller breeding tank, consider an air driven sponge filter<

Cleaning your Filter

Approximately once every 3 months, your filter should be disassembled and cleaned.  Start with a bucket of water from the aquarium.  This is critical as tap water contains chlorine and chloramine which are to kill bacteria.  The mechanical filter should be rinsed.  Put it in the bucket of water and slosh it around.  Your goal is to remove the large particles.  You do not want to completely clean it as this does harbor a lot of beneficial bacteria.

You should check how much activated carbon is still remaining in your chemical filtration.  Carbon will slowly decay over time as it interacts with compounds in your aquarium.  If it is running low, refill it.

Take all of the plastic pieces and rinse them in your bucket of water.  Wipe off any algae build up.  The main goal is to wipe off anything that could slow down the flow rate or could interfere with the normal operation of the filter.  This is also an aesthetic thing – making your tank look cleaner.