Types of Media Filters
Aquarium Undergravel Filters
The old standby. People either love them or hate them. Undergravel filters have huge surface areas for biological filtration and can be operated with either airstones and an airpump or powerheads. When using powerheads, remember to use the aeration feature on powerheads or an airstone. These systems are occasionally the only filters that will fit the application. The down side is without frequent gravel cleaning via water changes, undergravel filters are a problem waiting to happen. Always use additional filtration, whenever possible.
Aquarium Hanging / Box Filters
Probably the most sold type of filter. Although easy to both install and maintain, these filters require frequent cleaning and pad/sponge replacement. This is, however, a fairly easy task. Remember, these units hold the aquarium away from the wall 3-5 inches. For better water quality, opt for multiple box filters instead of bells and whistles. If one filter goes down, there is a backup. Never change both pads in a double padded filter or both filters in a dual box filter setup at the same time when cleaning. Alternating the media replacement preserves important bacteria. Some filters have room for additional bio media which should be used. Some have aeration features - moving surface water also aerates but remember, heavily loaded systems benefit from a decoratively placed airstone.
Prefilters fit most models and increase all aspects of filtration for these units while preventing small fish and invertebrates from being injured. Rinse these filters at the first sign of reduced flow. Multiple filters can be hooked together if flow is restricted or cleaning is required too often.
Aquarium Internal Filters
Many filters fall into this category. They include internal sponge, powered internal, and internal box or canister filters - air powered and motor powered. Breeders love them. They are easy, low cost, low hassle filters. They all aerate and biologically filter. The old fashioned, floss-filled internal air driven box or canister filter is great for breeding tanks, small tanks or for quarantine tanks. Internal filters can be packed with a range of filter media for biological, chemical or mechanical filtration depending on the application. Because they operate by forced air, they both aerate and filter the water. If a larger tank is having problems, add an internal filter filled with high quality carbon and floss. The disadvantage of filters in this class is size - they are simply too small to handle much fish load, must be hidden and take up floor space.
Aquarium Pleat Filter
Pleat filters are, with out question, the best form of mechanical filtration. If removing small particles prior to a UV sterilizer, carbon, or heater chamber is your goal, these are the type of filter you are looking for. Pleat filters, however, do come with a price. Most of the filters in this category require advanced installation abilities and are best suited for commercial or large scale use. They also are best used with some form of biological filtration and additional aeration. Large sand filters, while not actually pleat filters, are included here. When packed with sand, they are used for large scale mechanical filtration and they also have biological capabilities.
Aquarium Canister Filters
Canister filters are quiet running filters with high biological capacity and should be considered second choice to trickle filters. Canister filters have both pros and cons. The better designed units have good chemical filtration because no water by-passes the media. Canisters are also ideal for planted freshwater systems or when trickle filters are simply too large for the application. Canister filters provide long service life if packed properly with quality media and are economical to operate compared to box filters. Remember, these filters are closed systems and usually have lower flow rates. Use a small air pump and a decoratively placed airstone in aquariums without live plants or in saltwater systems without protein skimmers. Air pumps increase oxygen levels and act as a fail-safe in the event of a filter failure. Choose a canister filter one size larger than manufacturers recommend for heavily loaded systems or for saltwater. Larger filters are more efficient and have higher flow rates. Stay away from filters that use small internal baskets for media. Better units have either large internal baskets or trays and can be completely packed using 99% of their space for media.
Aquarium Trickle Filters
This is the most important decision keepers make. Saving a few dollars at this stage can mean countless dollars in fish losses. Underfiltered tanks cause problems again and again and make fish keeping a headache instead of a pleasurable, exciting hobby. Trickle filters are the best choice for tanks above 30 gallons. Good mechanical and biological filtration maintains robust oxygen levels and keeps harmful fish waste and other decaying debris from polluting the water and killing fish. Trickle filters, because of their size and expanded biological surface area, perform these tasks better than any other form of filtration and should always be considered the first choice. Trickle filters are more reliable and easier to maintain. Since there are no costly cartridges to replace, trickle filters are also more cost effective to operate.
Many odd filters with specific applications fit into this category. Surface skimmers and various filter add-on units are available to supplement the main filtration system. If you have a canister or box filter and want a surface skimmer or you are looking for more advanced odd filters look here.