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Selecting a Filter

Tip: All tanks need biological and mechanical filtration to maintain a healthy environment.

Three Types of Filtration
In aquariums there can be three types of filtration processes - biological, chemical, and mechanical. All tanks need at least somem form of biological and mechanical filtration to maintain a healthy environment. It's a good idea to understand the basics of each type of filtration so you can make an informed decision when selecting a filter.

Mechanical - Mechanical filtration involves the removal of particles of waste by passing water continuously through foam or other porous material. The filter traps particles of debris, and is periodically cleaned or replaced. Because solid waste is constantly being produced in your tank, a mechanical filter of some type is a must.

Chemical - In chemical filtration water is passed though material such as carbon, which removes at least some of the dissolved materials. Toxic metals, ammonia, and even odors can be filtered out chemically. While chemical filtration is not absolutely required, it can be useful combined with other filtration methods. Chemical filtration is particularly helpful when starting a new tank, because it can remove ammonia

Biological - Fish produce wastes which cannot be filtered completely using mechanical or chemical methods. Unless these wastes are removed, over time they will build up to a lethal level. In biological filtration, two types of beneficial bacteria known as "nitrofiers" grow in the tank and convert harmful wastes into something less harmful. All aquariums need to have successful biological filtration in order for the fish to remain healthy.Typically it takes about a month to establish a flourishing biological colony that will effectively filter all the harmful wastes

Tip: For the beginner 20-30 gallon tank I recommend a power filter.

Basic filter types include:
  • Box filters, Cannister filters (figure 1)
  • Fluidized bed filters
  • Power filters (figure 2)
  • Sponge filters
  • Underground filters (UGF)
  • Wet/Dry filters (figure 3)

    When making a choice keep in mind that you need to accomplish at least mechanical and biological filtration. For small tanks (ie 10 gallon and under), corner "box" filters that sit inside the tank are generally used. They can provide both mechanical and chemical filtration depending on what you put into them. For mid-size tanks a power filter or UGF is generally used. Power filters can be filled with materials that provide both chemical and mechanical filtration. UGF filters provide mechanical and biological filtration, however they can be more prone to unseen problems (ie: blockages, loss of bacterial colonies). For that reason I personally recommend power filters over UGF's for beginners. For larger tanks (50 gallon and up), cannister filters are often used. They can provide all three types of filtration, depending on what is put in the cannister.

    Figure 1
    Figure 2
    Figure 3

    Tip: Flow rates are good to consider

    Flow Rates
    One factor not often mentioned, but which does impact the success of your filtration system is the rate at which water flows through it. The rule of thumb is to run all the water in your tank through the filter at least four times each hour. That makes it pretty easy to calculate what you need. When it's borderline, always move to a higher flow rate. So if you have a thirty gallon tank and the shop only has power filters rated at 100 or 150 gallons per hour, you should purchase the larger one.

    Tip: Combine a sponge with your filtration unit

    Box and Power filters don't support biological filtration as naturally as other filtration types. One way of enhancing them is to add sponges, which will provide more space for the beneficial bacteria to grow. Round or square sponges are made to fit the intake tubes of a power filer, or attach to an airline. Small star shaped sponges are made for placing inside the box, and do an excellent job of supporting biological filtration. You should be able to find both of these at a pet shop. Remember... these will need to be cleaned from time to time.

    Tip: Whenever possible get filtration media in separate packages.

    We have learned that it's cheaper to purchase virtually anything in bulk. But when it comes to activated carbon or other absorptive filtration media, it's best to get it in smaller quantities. Better yet are individually sealed units that aren't opened until they are used. The reason is that these materials begin absorbing odors and moisture from the air as soon as they are opened. If you buy a large volume, the material that isn't used will begin to deteriorate once the package is opened. If you do buy in bulk, seal the unused portions in airtight containers to preserve it.

    * Art and photos are the property of Shirlie Sharpe. If you use them please write for permission.

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