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Filtering Aquarium Water


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For aquatic animals, good water quality is synonymous with good health. Good water quality is dependent on efficient filtration of the water in your tank. Understanding filtration is one of the most difficult tasks facing the new aquariust.

Even the novice aquarist is aware that high levels of ammonia will quickly spell the end to her fish. Unfortunately, many water quality problems are more subtle. There is a domino effect set in motion with deteriorating water quality, ending in the death of a tank full of pets.

As water quality slowly worsens, the fish suffer from physical stress. Stress, over time, will cause the health of the fish to decline. Chronic stress makes fish vulnerable to bacterial and fungal infections and parasitic infestations. These infections and infestations will be but the conclusion to the phenomenon that began with poor water quality caused by inadequate filtration.

An appropriate filtration system and good aquarium management can minimize, if not completely eliminate, chronic stress. To better illustrate the correlation between fish health and filtration, a discussion of the three basic types of pollutants that accumulate in aquarium water and the corresponding filter options for each kind is appropriate.

Particulate Pollutants

There are a number of sources for the particulate matter that accumulates in aquariums: uneaten fish food, digested waste products, and cell material from fish and plants. Some of this material remains in suspension rather than sinking to the bottom, making the water turbid - cloudy and dirty.

Larger particles sink to the bottom, only to rise again and cloud the water when disturbed by fish or aquarium maintenance activities.

Besides being aesthetically unappealing, fish and plants are adversely affected buy turbid water. Turbidity-induced stress weakens the ability of fish to resist the disease organisms that are a normal part of the aquatic environment. Gill filaments may become irritated and begin to swell interfering with respiration, which heightens stress, and eventually causes gill membranes to become susceptible to bacterial and parasitic invasion. Deposits of particulates on plant leaves reduce light adsorption and gas exchange, and many plants will die as a result. Finally, suspended particulates may also support blooms of disease-causing bacteria.

Daily water changes of about one-fourth of the tanks water and an in-tank gravel cleaning, would reduce particulate pollution. Who has time for that? (Not to mention, too much new water can be quite stressful to some fish.

The best way to deal with suspended material in the water is with mechanical filtration. This works by collecting particles from the water as it continuously circulates through a mechanical screening medium. Mechanical filtering mediums include nylon or polyester floss, foam sponges, fiber pads, aquarium sand and diatomaceous earth.

These media differ primarily in terms of the size particles they can effectively capture, their cost, service life, and reusability. At one extreme is floss, which tends to trap only the largest particles and cannot be reused, but is inexpensive. At the other extreme is diatomaceous earth, which can trap extremely fine particles but is expensive and requires the most maintenance.

The size of the spaces - or pores - in the media, the shape of the spaces, and the roughness of the material determine the particulate-trapping ability of mechanical filtering media.

Filtering medium that traps very fine particles will quickly clog and requires frequent replacement. Otherwise, the water flow will be restricted to the point where turbidity in the tank actually increases! A better method is to use filter material that traps larger particles, such as fiber pads. Over time, the accumulation of larger particles fills in the spaces, and smaller particles are also trapped. When the water flow of the filter is significantly reduced, the filter media is then cleaned or replaced.

An important factor in choosing the mechanical filter is the rate at which the water will flow through the material. An outside power filter should circulate, in gallons per hour, four to six times the volume of the aquarium in gallons. Thus, for a 50-gallon tank, the filter should process at least 200 gallons per hour.

When choosing from among several filters of the same flow rate, note which design offers the largest filtering-medium surface area.

Organic Pollutants

A variety of substances such as proteins, amino acids, and other metabolic byproducts are continuously being discarded into the aquarium water by the fish. These organic substances are dissolved into the water - thus the name, dissolved organic carbon (DOCs).

If these DOCs are allowed to become concentrated in the water, the health of the fish will suffer.

DOC concentrations can be controlled by 50-percent water changes every day. NOT.

The practical way to deal with DOCs is by chemical filtration techniques that are reliable and economical. The most common and reliable are carbon filtration and protein skimmers (foam fractionation).

Carbon filtering removes DOCs via adsorption. As the aquarium water flows through the carbon medium, the DOCs come into contact with the surfaces of the carbon granules and become attached. Some DOC compounds are adsorbed directly, whereas others combine chemically with already-captured substances.

When the surfaces of the carbon become saturated, it must be discarded and replaced with new carbon.

Many types of carbon are sold for aquarium use, but only a few are actually capable of adsorption in water. The material of choice is high quality granular activated carbon (GAC). This is carbon that has been degassed in an oxygen oven at temperatures close to 2,000 degrees Fahrenheit. The degassing enlarges the apparent surface area of each carbon granule, greatly increasing the adsorptive capacity.

In a filter, the GAC should always be placed after the mechanical filtering medium. Otherwise, the particulates in the water will quickly coat the surfaces of the GAC, rendering it useless. Deep beds of GAC are always more effective than shallow ones of equal area. Using the smallest granules available maximizes adsorption.

Do not use powdered activated carbon. It compacts too easily and seriously restricts water flow except in specially designed systems.

There should be 4 to 10 grams of GAC for every gallon of water, and it should be replaced monthly. Choose the best quality GAC you can find. Any chamber that houses less that 4 grams per gallon of water is useless and will only work to restrict water flow.

The most common use of a protein skimmer is in saltwater aquariums, but they work just as well in freshwater tanks. The only difference is that the freshwater aquarium must be set up and running for a while before a protein skimmer works as designed. GAC beds and protein skimmers remove such substances as hydrogen sulfide, and other certain toxic chemicals that may find their way into the aquarium. Unfortunately these devices are incapable of telling the bad guys from the good guys and will also remove beneficial chemicals, such as many medications. Therefore, it is imperative to remove all GAC from the filter and shut off a protein skimmer before medicating fish.

Continue to Part 2.