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Aquarium filters are available in all types and shapes to suit any need. A good filter will provide for high water quality and keep the water crystal clear for viewing. An aquarium is a closed system and must be maintained by you, the hobbyist to optimum conditions. To achieve this ideal situation, the right size and type filter must be used.
Before you buy a filter you should understand three different types of water purification, I will explain them here before going on to the different kinds of filters.

  • Mechanical
    This is simply the removal of suspended particles of waste, excess food, plant matter and general dirt from the aquarium.
    Most filters employ some sort of mechanical filtration through filter floss, pads or sponges that trap the waste as water passes through it.

  • Chemical
    This is achieved through the use of various media or resins placed in the filter. This media removes dissolved waste materials such as fish waste, etc., that can cause odors and discoloration of the aquarium water. Chemical media placed inside the filter can also remove Phosphates, Nitrates, Ammonia and many other toxins. The most common form of Chemical filtration is the use of activated carbon.

  • Biological
    The most misunderstood type of filtration, Biological filtration is the process in which beneficial bacteria convert organics that have been broken down into the toxic elements of Ammonia and Nitrite into the less harmful compound Nitrate.
    Nitrate can then be removed by water changes or chemical means. The process of Biological filtration does not happen fast and usually takes between four to six weeks to be established. The bacteria will colonize all surfaces of the tank and filter. Some filters are designed to promote these bacteria through the use of special media. Most complaints of cloudy water are due to lack of a good bacterial filter, which causes the bacteria to float freely around the tank.




There are many different types of filters available including:
  1. Canister
  2. Power
  3. Undergravel
  4. Wet/Dry
  5. Submersible
  6. Diatom

I will explain each type here.

  • Canister

    These are usually placed under the fish tank, hidden in the stand. There are available capacity sizes from ten to hundreds of gallons. They provide Mechanical and Chemical filtration and some have compartments for Biological as well.
    Hose intakes and returns connect the filter to the tank and can be isolated through the use of valves. These filters can run a long time between cleanings and maintain great water quality and are virtually silent. My personal favorite are the filters made by the Eheim Company

  • Power Filters

    These are probably the most common of aquarium filters. They are easy to install and maintain and provide both mechanical and chemical filtration. Some newer types also provide for biological filtration.
    These filters move large amounts of water and do a fine job of filtration. They all hang on the back of the tank and are generally shaped like this (square). All power filters are a good choice for the new hobbyist.

  • Under-gravel Filters

    The sole purpose of this filter is to provide biological filtration. It is a series of plates put under the gravel and water is drawn through it, either by an air pump or power head. An additional filter must be used to provide for mechanical filtration. This type of filter has fallen out of favor, but still does its job and should be considered.

  • Wet/Dry

    The latest rage in filtration, the wet/dry provides all three types of filtration. It is large open filter that sits under the tank and has sections for each of the types of filtration. You can even place the heater in the sump of the filter.
    Wet/Dry filters are mostly used by the mini reef community as their higher water quality needs are met by this type filter. These units usually do not include all needed items, pumps etc. Once set up the maintenance of these filters is easy.

  • Submersible Filters

    These are small specialized filters that mount inside the tank. They mainly provide mechanical filtration and circulation and can be used in hospital or fry tanks. The units must be removed from the tank for cleaning, making them not the most convenient filters to have. They do have their uses and should be considered under certain circumstances.

  • Diatom Filters

    These are highly specialized filters used to "polish" the water. They use Diatomaceous earth powder to coat a filter bag and filters water down to microns in size. Due to the high efficiency of these filters, they are to be used only sporadically and for short periods of time. If you have more than one aquarium a Diatom filter is a good thing to have.


Now that we have discussed the various types of filtration and filters, what do we put in them? I have mentioned the term filter media before, here I will explain in a little more detail.

There are a large amount of filter media available from almost every aquarium product maker, for every type of filter. There are so many, that the choice of which ones to use can be very difficult and sometimes frustrating to find the one which will do what you want. I will describe the three type of media here in generic terms.

  • Mechanical Filtration Media.
    This media is used to remove all sizes of free floating waste material from the tank water. There are many kinds available, but they all serve the function stated above. Some of the more common types are:
    1. Floss
    2. Sponges
    3. Pads
    4. Sheets

    The mechanical filter media should always be placed first so that any aquarium water must pass through it before the more expensive media. Many filters come with custom made filter replacements that fit perfectly and make replacement very easy.

  • Biological Filtration Media
    This media purpose is solely to provide a large surface area to promote the growth of the beneficial Aerobic bacteria. This bacteria is responsible for the nitrogen cycle and breaks down the deadly Ammonia and Nitrites into the less harmful Nitrates. It to comes in many different forms, all with a large surface area to size ratio. Some common shapes are:
    1. Balls
    2. Tubes
    3. Spheres
    4. Beads
    5. Cubes

    Biological filtration is the most important form of filtration for without it, the accumulation of fish waste will rise until the levels reach a point where fish can no longer survive. The media is usually placed in the filter after a good mechanical pre-filter to maintain cleanliness.

  • Chemical Filtration Media
    These media are designed to remove dissolved compounds that are not wanted in the aquarium water. Each media is designed to remove a specific compound and sometimes are combined together to make super cleaners. Some of the compounds that can be removed through Chemical media are:
    1. Odors
    2. Colors
    3. Ammonia
    4. Nitrite
    5. Phosphates and Nitrates

    The media usually come in their own bag and are placed in the filter after the Mechanical media. They remove the compounds in one of two ways, Absorption or Adsorption . Both ways provide high quality filtration and can reduce the number of water changes, while at the same time providing your fish with a cleaner healthier environment.