• You want your aquatic pets to be healthy, but you also want an attractive aquarium setup. Determining which filter or filters will work best for your tank will help you achieve a well-designed tank that harbors a healthy living environment.
  
  

Skimmer Filters

• Skimmer filters help to remove undesirable proteins commonly found in saltwater, or marine, fish tanks. These filters are not used in freshwater fish tanks but make great supplemental filters for marine tanks.
  
  

Sponge Filters

• A sponge filter is commonly used for hatching fry. These filters provide gentler suction than some other types, so the tiny fry are less likely to get sucked up. Sponge filters are also commonly used in tanks smaller then five gallons. If you are not using a tank like this or trying to hatch fry then this type of filter should not be used.
  
  

Hang-on-Back Filters

• Hang-on-back filters are most commonly used in freshwater tanks for which carbon filters are preferred. They get their name from the fact that the filter housing hangs off of the back of the tank and the water is sucked up through via a tube that extends into the tank. The water passes through one or more filters before being cycled back into the tank. This is a great filter to use for freshwater tanks because they take up little room, can be hidden behind the tank and provide excellent filtering of contaminants. They are less common in marine tanks since most marine tanks do not require carbon filtering.
  
  

Under-Gravel Filters

• The under-gravel filter consists of a grated plate that sits under the tank's gravel. The gravel acts as the filter medium. The filter is powered by a small air pump that pulls the water down through the gravel. This type of filter is often used in conjunction with a hang-on-back filter, since the under-gravel filter requires routine cleaning to avoid tank pollution. This filter is adequate for tanks up to 20 gallons. A tank bigger than that will require additional filters to help support the environment. Some hobbyists prefer to use two hang-on-back filters instead.