Picking an aquarium filter can be a confusing experience. With so many types on the market today, research is a requirement for a proper filter for your tank. We have outlined the major filter types available.

Canister Filters: Canister filters are excellent filters for the majority of aquariums. Many offer the ability to interchange your filtration media, allowing complete customization of your aquariums filtration needs. They work by bringing water out of the aquarium and into a pressurized "canister". The water is either pushed or pulled through multiple layers of filtration and then returned to the aquarium. This efficient design means less water gets unfiltered due to bypass. They are also useful in powering a UV sterilizer or other accessory. The main downfall of canister filters is low biological activity (not including Eheim wet/dry canisters). Since the units have to be cleaned, and most of your filtration media is changed regularly, most bacteria is periodically purged from them.

Freshwater - Canister filters are perfect for freshwater aquariums. On a small to medium aquarium, one canister such as the Magnum series should be all the filtration needed. On larger aquariums, a modular canister system such as the lifeguard would be excellent and provide crystal clear water.

Saltwater - Canisters make a great part of a saltwater filter system, but a secondary biological unit is usually required. Without a good biological bed filter, a saltwater aquarium will frequently experience high nitrite and ammonia problems, and a much shorter inhabitant life expectancy. Adding an Undergravel or bio-wheel filter will fulfill this necessity. Canisters are also excellent as a secondary filter and spot cleaner on a wet/dry. One exception to this rule is the Eheim Wet/Dry Canister filters that are excellent as a complete filtration solution for marine aquariums.

Mini-Reef - Canisters work great with mini-reef systems, but care is needed in picking the chemical media as some will leech out needed trace elements. The Eheim wet/dry filters are excellent for use in a small to medium sized reef aquarium. Standard canister filters are better for spot cleaning or specialized media containment.

Hang on Tank Filters: Hang on tank filters offer a good compromise between economical operation and high grade filtration. They work similar in fashion to canister filters but are usually not pressurized (the HOT magnum is a canister filter and is pressurized). Water is pumped into a box on the back of the tank and then allowed to run through a cartridge, or in the Magnum, forced through a set of media. The water is then returned to the aquarium.  As a low cost alternative for canister and wet/dry filters, they do have limitations. Water by-pass can (and does) occur with cartridge filters, and the media selection that can be used is fairly low. Flow rates are low and highly variable depending on how clean the system is. On a high note, hang on tank filters are highly versatile, and very easy to maintain.

Freshwater - Perfect as a low cost filter for freshwater. All but a protein skimmer type would make an excellent choice. The Emperor series is an excellent filtration system for small to medium freshwater tanks and offers complete mechanical, chemical, and even biological filtration.

Saltwater - Hang on back filters are great as part of a complete filter system. The emperor is a decent filter for a small to medium saltwater aquarium. Other hang on tank filters are not as efficient and low bio-activity combined with water by-pass could be costly in aquarium life. Combined with a proper bio-active filter such as a wet/dry, sand filter, or Undergravel, a hang on tank filter can become a valuable addition.

Mini-Reef - Good as a spot filter or secondary filter unit, hang on tank filters do not offer the flexibility needed for a true mini-reef. Not recommended.

Wet/dry or Sump Type: Working on the same principal as an undergravel filter, water is passed across colonies of bacteria, which breakdown harmful ammonia and nitrite. Water is then put into a sump area. The addition of a sump to an aquarium allows you to add high-end protein skimmers, UV sterilizers, and much more to your tank easily. It is recommended that a minimum of gravel be used in a wet/dry filter aquarium. A thick layer of gravel will hold more dirt and require more maintenance. A properly setup aquarium with a wet/dry has very low maintenance and high inhabitant life expectancy.

Freshwater - At the top of the chain for freshwater is a wet/dry. Healthy fish, cleaner tanks, and more time between cleanings are what this filter will offer the average freshwater aquarium. Less gravel means few gravel cleanings. Not recommended for very dirty fish, such as Oscars because of the high-organic content they release.

Saltwater - Excellent for saltwater as well. Fish will display more natural, vivid colors and stay healthier. Less gravel, and no Undergravel to hold dirt. A good carbon filter for spot cleaning is helpful. Less water changes in saltwater means less maintenance and less shock to your inhabitants.

Mini-Reef - Good with proper care, more useful for the sump it creates than for filtration in a proper mini-reef. Most bio activity should be found in your live rock. A wet/dry can be an integral part of a mini-reef system when used correctly. A protein skimmer in the sump for a mini-reef is a must, and a good de-nitrification system is helpful. With these items in place, water chemistry can be stable which will help your live coral to grow and thrive.
 
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