Commissioner Adam H. Putnam

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Aquarium Fish

Aquarium Components: Filtration

Filtration is a very important aspect of an aquarium system. Filtration is comprised of three main components: mechanical, chemical and biological. Sterilization using ultraviolet (UV) or ozone systems can also be added.

Mechanical Filtration: Mechanical filtration traps larger, suspended solids with the use of materials such as floss or foam. Regular maintenance of these materials must be performed to keep the material from clogging and reducing or eliminating its effectiveness.

Chemical Filtration: Chemical filtration uses adsorption (the process of binding particles to a surface) to remove some dissolved substances from the water. Activated charcoal is often used for chemical filtration because it is very porous and, therefore, has a large surface area. Resins and clays are also used. However, it has a limited life span and, regardless of its purpose, must be replaced on a regular basis.

Biological Filtration: Biological filtration is the process in which ammonia, which comes from fish waste and is highly toxic to fish, is converted to nitrite (also toxic to fish) then to nitrate by beneficial, nitrifying bacteria. Nitrate is far less toxic to fish, except in extremely high levels. This process is known as nitrification.

A variety of filters are available on the market, many of which incorporate more than one type of filtration. Additionally, a combination of filters may be used to maximize the strengths of different filters.

Sponge Filters: A sponge filter is a simple design that uses an air pump to circulate water through a sponge sitting inside of the aquarium. The foam sponge will trap solids (mechanical filtration) and provide some biological filtration as bacteria grows on the abundant surface area of the sponge. This fairly limited type of filtration is best for smaller tanks and those less densely stocked with fish.

Under-Gravel Filters: An under-gravel filter uses an air pump to create an air lift, constantly pulling water down through a slotted plate under the substrate and circulating the water back up to the top of the tank. This type of filter works as a mechanical filter by trapping solids in the substrate as the water moves down through the substrate and filter. It also works for biological filtration by using the aquarium substrate as a surface for growing the nitrifying bacteria. An under gravel filter must be cleaned regularly by siphoning the bottom of the tank to remove the trapped solids.

Accumulated solids contribute to degradation of water quality including an increase in ammonia, decrease in oxygen and promotion of the non-nitrifying bacteria. An under-gravel filter can be set up with reverse flow (water travels up through the filter and substrate), which makes cleaning easier.

Power Filters: A power filter incorporates primarily mechanical and chemical filtration. Water is pulled out of the tank into the filter and, generally, forced through a bag of closed-webbed floss that traps the larger solids. The bag is often filled with activated charcoal that adsorbs many of the dissolved substances as well. Some biological filtration will also occur as the nitrifying bacteria grow on the floss bag. The bag, however, must be rinsed or replaced on a regular basis to prevent clogging, thus losing the bacteria. Most of the biological filtration for this type of system occurs on the substrate of the tank. Although most power filters hang on the back of the aquarium, internal tank power filters are also available.

Canister Filters: A canister filter forces water through a variety of media and can incorporate mechanical, biological and chemical filtration. A trickle filter works in much the same way but water generally passes with less force. Since none of the media move, a thick bacterial film can quickly develop resulting in the need for frequent cleaning.

Fluidized Beds: A fluidized bed is one which keeps the media, often silica sand or resin beads, "fluidized", or in constant movement through rolling water. This movement continually shears off excessive bacteria. Bead filters can incorporate both mechanical and biological filtration. However, sand filters must have a mechanical filter in line before it to prevent clogging the fine sand. Fluidized bed filters are one of the most efficient biological filters available.

Rotating Biological Contactors (RBCs): A rotating biological contactor (RBC) has a wheel which constantly rotates alternately exposing itself to tank water then air, which provides the oxygen critical for nitrifying bacteria growth. The rotation of the media through the water removes excess and competing bacteria from the wheel.

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