Saltwater Aquarium Filtration

Filtration

Filtration is arguably one of the most important considerations for maintaining a successful aquarium. Keeping your pets' water clean and free of dangerous chemicals and parasites is absolutely essential to their health and lifespan. Choosing the right filtration equipment should therefore not be taken lightly. There are two basic filtration methods which I'll discuss below.

Mechanical Filters

Mechanical filters typically hang on the back of your tank and draw water from the aquarium up though a tube into the filtration unit. The water is then forced through media which usually consists two components. First the water flows through a cotton or polyester filter which traps and removes free floating particles, such as uneaten food. Then, the same water flows over or through a layer of activated carbon or charcoal. Activated carbon is extremely porous and can absorb the tiny dissolved organic materials that accumulate in the aquarium which would otherwise quickly pollute the tank

Biological Filtration

Biological filtration is a chemical reaction that takes place in the bed of gravel in the bottom of your tank. Over time, bacteria will colonize on the surface of the pieces of gravel or substrate material in the filter bed. The filter bed is composed of this gravel substrate and an under gravel filter. This under gravel filter should cover the entire surface of your tank floor and then be covered with about 3 inches of substrate material (gravel.) This substrate material is readily available at your local pet shop and generally comes in two types, crushed coral or dolomite. Both of these materials have a very high calcium content which is essential in maintaining the proper PH level in your tank (more on this later.) Neither material has a real advantage over the other. Crushed coral is usually slightly more expensive but some aquarists find it to be a more attractive substrate.

Attached to this under gravel filter is a vertical tube which will extend nearly to the top of the tank. You will attach a pump, typically called a power head, to the top of this tube. This pump acts as the mechanism to draw water from the tank down through the gravel, into the under gravel filter, up through the tube and back into the tank. This process serves two purposes. Solid, free floating particles are trapped in the gravel bed as the water is drawn through it. Additionally, the various bacteria that colonizes on the gravel provides chemical filtration. The basic chemical filtration process is a three step process:

Animal waste products, leftover food and other organic materials in the aquarium decompose producing ammonia. This is extremely toxic to the animals in your tank and will quickly kill them if the level of ammonia in the tank rises too high.
One type of bacteria in the gravel bed converts the ammonia to another chemical called nitrite. Nitrite is also toxic, although less so than ammonia, but will also lead to the demise of your animals if not removed.
A second type of bacteria in the gravel bed then converts the nitrite to another chemical, nitrate. Nitrate, although not immediately toxic to most fish, is not well tolerated by some of the more delicate sea creatures such as corals and invertebrates. Nitrate will gradually accumulate in your tank and can only be effectively removed by regular water changes.

When you're done here, check out some of these other aquarium sites:
Katy's Tropical Fish
Angelfish Revealed
SaltWater Aquarium Advice
Tropical Fish Secrets
Aquatic Experts
Starting A Reef Tank