Filtration Basics: The clear waters in and around the natural reefs are a key part of survival for the inhabitants there. Every creature on the reef depends on water that is clear of ammonia, nitrites and nitrates. Due to the overwhelming size and bulk of biological filtration, the water in the ocean remains very stable when compared to the water of an aquarium. Water filtration for an aquarium is one of the most important factors to plan for when designing and setting up a system. There are many different types and sizes of filters starting with the basic hang on back (HOB) filters and ranging all the way up to high tech protein skimmers. This article will cover some of the more basic of aquarium filters such as: HOB, canister and wet/dry filters. Methods of filtration are divided into three main categories. Mechanical filtration is the use of sponges or filter floss to physically remove particles from the water. Most filtration devices use this method first to keep bio and chemical media clear of debris. Bacteria can also be used to filter chemicals such as ammonia and nitrite from the water. This is called bio-filtration. Many media cartridges come with bio-media such as: bio-balls or ceramic rings to act as a habitat to filtering bacteria. The final method of filtration is called chemical filtration. There are several types of chemical filtration cartridges available that can help remove toxins, smells and also clear up the water. HOB Filters: HOB filters are a great way to get started developing your filtration system. The basic design of an HOB filter is a siphon tub that hangs down into the water, a pump to draw water up the siphon tube and a media box that overflows back into the tank You can find this type of filter in many different sizes to suite most aquariums. The media compartment holds premade filter cartridges containing mechanical, bio or chemical media. Some HOB’s also include a wet/dry bio-wheel which acts as a very strong bio habitat. Regular maintenance is recommended to keep HOB cartridges clear of debris. Canister Filters: Canister filters work in much the same way as HOB filters. A siphon tube is put in the display tank water to transport water to the filter. Attached to this tube is a hose that is run to the canister filter. This is where the motor which moves the water through is housed. The water is pushed through a series of filtration chambers within the canister, and then pushed through a second hose back into the display tank. The biggest advantage a canister has over a HOB filters is space for more media. Canister filters typically can hold more volume and variety of filtration media. The most common configuration of media within a canister filter is: mechanical filtration, bio-filtration and finally chemical filtration. Like with HOB filters maintenance is required to keep the media clean. Wet Dry: The final and most efficient of the basic filters is the wet dry filter. A wet dry filter is similar to a canister filter in the way that it is located remotely from the tank and uses hoses to transport water to and from the tank. A wet dry filter however uses an overflow and gravity to feed water to the filter. A wet dry set-up starts with a drilled or HOB overflow which gravity feeds water to a trickle plate. This trickle plate spreads water out over a chamber filled with bio-balls. Water is allowed to trickle through small holes evenly over the bio-balls. It is considered a wet/dry because the bio-balls are not submerged, but trickled with a steady flow of water. This is the perfect habitat for the most powerful ammonia and nitrite processing bacteria to thrive in. After the water leaves the wet/dry chamber is collects in the chamber which houses the return pump to be pumped back into the display tank. As with HOB and canister filters wet/dry filters need regular maintenance. The bio-balls should regularly be rinsed in tank water (never fresh water).