Types of Filter

Box Filters

The filter is simple and efficient for small aquariums and fish bowls. One filter is perfect for your 10 gallon (or smaller) tank.  They are plastic boxes fitted with a perforated lid and a lift tube.  

The lift tube connects to an air hose, and the bubbles rise up the tube from the bottom of the box. Filtration media are packed around the lift tube, filling the box.  Water flows down through the media and up the tube, drawn by the rising stream of air bubbles.  The bubbles help to aerate and oxygenate your tank. 

A simple design and efficient filtering.  Easy to assemble and simple to use.



Canister Filters

These are external fish tank filters.  The ideal solution for maintaining a large aquarium where a strong water current and high level of filtration is necessary.  These include supplementary media such as carbon.  External filters also contain a greater amount of sponge and biological media, enhancing the level of mechanical filtration and breakdown of ammonia.  Canister filters have an integral water pump.

Their main appeal is that all of the water is forced to flow through all of the media.

Our article ‘The Benefits of Canister Filters’ gives you lots more information, go here to read it.


Chemical Reactors

Chemical reactors or ‘aquarium reactors’ are chambers in which aquarium water ‘reacts’ with some medium to alter the water chemistry, either adding substances to the water or removing them.  As long as it is a chemical reaction, and the medium is freely mixing with the water, the device is called a reactor.  These reactors are designed to optimize the contact time between the water and the surface area of the reactor media. They take full advantage of the entire capacity of the media.


Two common examples are calcium and phosphate reactors.

In the first, a calcium carbonate medium and carbon dioxide gas are mixed. The water leaving the reactor is higher in calcium and alkalinity than the water flowing in. This maintains the high levels of calcium needed in tanks with growing corals and clams.

Phosphate reactors circulate the tank water in a chamber with a phosphate-removing medium; such as granulated ferric oxide (GFO), an aquarium reactor media that is great at removing phosphates and silicates from your aquarium water, two water pollutants that are exceptionally “helpful” in growing problem algae in your tank.  GFO granules have a high surface area.  Reactions typically occur on the surface, so more surface area means more room for reactions, which in turn means more capacity for filtration.  The use of a phosphate reactor can keep phosphate levels from rising.

Granulated ferric oxide (GFO) is sold under a few popular trade names you may have seen before:

  • Phosban
  • PhosphateOut
  • Phospure
  • RowaPhos


Filter Media

Most filters are modular, this allows them to be combined to suit your particular tank needs.


Filter pads have bonded fibers that effectively trap uneaten foods, waste excreted by livestock, decaying plants, detritus, dust, and other floating particulates from aquarium water. The design allows maximum flow and keeps the pad from clogging too quickly while keeping your aquarium water crystal clear. 

They are great value and offer consistent and repeatable filtration performance in freshwater and saltwater aquariums.   Filter pads are typically used as a pre-filter for wet/dry filters, sumps, and canister filters to clean water in freshwater, saltwater and reef aquariums.

Activated carbon is universally available for refilling carbon fine mesh bags.  Many of the major filter manufacturers sell bags to fit their filters. Carbon is used to remove odors, colors and impurities including yellow-brown tint, toxins, chlorine, most medications and some heavy metals.

Other medium  options include zeolite for ammonia removal, resins for phosphorous removal, ceramic for biofiltration surface area, and empty modules you can fill with whatever media you like.

Many manufacturers offer modules in a gradation of weave or pore sizes so that you can stack them from large to small to trap increasingly finer particles. This also provides an efficient pre-filter to prevent the pores of a biomedium from becoming plugged.

Click this link to see all Filter Media on Amazon.com.


Outside Filters

Very common today is the hang-on-back (HOB) filter. These filters are made to hang on the back of your aquarium, and provide excellent mechanical and biological filtration. They are ideal for use in tanks where space is limited inside the tank, and remove the need for unsightly filters in the tank itself. 

They use a pump to suck water up a supply tube from the aquarium. The water then flows through a series of compartments with various media and back into the tank via an overflow.  


Sometimes the flow of the water back into the tank can appear as a waterfall creating surface movement and aeration, resulting in healthy oxygen levels. it adds oxygen as it falls back into the tank. 

These filters are available in a full range of sizes. A simple guide is to select a filter with a flow rate at least six times the volume of the tank—so for a 30-gallon tank you want a flow rate of about 200 gph (gallons per hour).

Very popular are the Tetra Filters – to see our article, click here

One of the best filters for small tanks is the Finnex PX – see our review click here.

Protein Skimmers

Protein skimmers are used in saltwater setups to remove dissolved substances before they begin to break down. Some models stand alone (or hang on the tank) with their own water pumps, and others are designed to operate in a sump, utilizing the sump’s plumbing and pump.


Water is pumped through a tall vertical column in which air bubbles are rising. The air can be supplied by an air pump or by a water pump with venturi, which is a valve that draws air into the water stream. The basic principle here is to get air bubbles into prolonged contact with the tank water. Polluting substances are attracted to the air-water interface of an air bubble. These concentrate in the bubble stream, rising with it and appearing at the top as foam. The foam continues to rise into a collection apparatus, while the water flows back into the tank. 

These are simple to set-up, easy to clean.  Available for nano tanks upwards. Seen as having good  energy efficiency, delivering very effective organic waste removal.

Sponge Filters

A sponge filter is usually as simple as a sponge attached to a riser tube. Water is drawn through the sponge and out the other end of the tube, either by airlift or by powerhead. Simply connect the unit with an air pump thru airline tubing and provide both aeration and filtration for your fish.


These filters are perfect for Fry Betta Shrimp tanks, and they are easily cleaned by gently squeezing the sponge in a bucket of tank water.

Sponge filters are extremely useful, but they aren’t decorative, so they are much more often used in breeding and rearing tanks rather than in display setups.  These sponge filters do not trap fish fry and are safe for small size fish like dwarf cichlid, guppy, killifish, etc. They are useful as a breeding filter or as a secondary filter. Or they can be used as pre-filtration unit by fitting to an external or a top filter.


Trickle Filters

Trickle or wet-dry filters drip or spray aquarium water over a medium for marine and freshwater aquariums. This maximizes oxygen saturation and provides excellent biofiltration.  The filter box is placed on top of the aquarium.


Water is pumped over a number of perforated trays containing filter wool or some other filter material. The water trickles through the trays, keeping the filter wool wet but not completely submerged, allowing aerobic bacteria to grow and aiding biological filtration. The water returns to the aquarium like rain.

These units are extremely efficient at converting ammonia to nitrate. They provide a large surface area for beneficial bacteria colonies to grow.  They are also known as nitrate factories – avoiding nitrate build up is extremely important.


UV Sterilizers

Rather than removing or adding substances, an ultraviolet (UV) sterilizer kills living organisms. Tank water is circulated through a chamber exposed to UV radiation from a special bulb. The longer the water is in contact with the UV radiation, the better.  The submersible UV sterilizer allows simple and effective UV control of harmful microorganisms & free-floating algae.


UV sterilizers are indiscriminate—they kill all living organisms, from algae cells to pathogens. Thus, they are widely used to control disease.

For use in fresh or saltwater aquariums and garden ponds.  When properly matched to the aquarium size they can destroy any free-swimming pathogens or parasites. In pond setups they are often used to control greenwater algae blooms.   

To be effective you must change bulb yearly for optimum UV performance.


Fish Tank Selection

If you are new to keeping fish and want help selecting your aquarium / fish tank and the stand, along with breeding tanks should you wish to get a little more serious about being an aquarist, then we strongly recommend that you look at our pages:

  1. Fish Tanks and Stands
  2. Aquarium Starter Kits
  3. Breeding Tanks
  4. Fish tank – up to 5 Gallons