Chemical Aquarium Filtration - Underwater Eco Systems

Chemical Aquarium Filtration

Chemical filtration, in short, is the removal of dissolved wastes from aquarium water. Dissolved wastes exist in the water at a molecular level, and fall into two general categories, polar and nonpolar. The most common chemical filtration method involves filtering the water through gas activated carbon which works best on the nonpolar wastes (but also removes polar wastes). Another effective method is protein skimming, which removes polar wastes such as dissolved organics.

Granular activated carbon (GAC) is manufactured from carbon, typically coal, heated in the presence of steam at very high heat. This process causes the carbon to develop huge numbers of tiny pores, which trap nonpolar wastes at the molecular levels by means of adsorption and ion exchange, and removes heavy metals and organic molecules, which are the source of undesirable colors and odors, through a process known as molecular sieving.

The best GAC for filtering water is made from coal and is macroporous (having larger pores). A good macroporous activated carbon feels light (not dense) and fizzes and floats when initially wetted. GAC intended for removing wastes from air (such as odors) are commonly made from coconut shell and are microporous. Carbons for filtering air feel more dense.

Some people (especially those with reef aquaria) are concerned about phosphate leaching from activated carbons. As a rule, buy only carbons made by reputable aquarium supply companies which have been acid washed during manufacture to minimize ash content. Carbons low in ash also help reduce the chance of undesirable pH shifts. Low ash carbons typically have lower phosphate leaching levels too.

The phosphate in GAC stems from the fact that activated carbon is manufactured from coal, which was once living plant matter. All living matter is high in phosphates. The leaching of phosphate from GAC is known to be high initially and to decrease over time. This problem can be mitigated significantly by presoaking your activated carbon for a few weeks before use.

Some people are concerned about GAC removing trace elements required by plants and invertebrates for healthy growth. Trace element depletion is a problem in planted aquaria and minireefs, with or without activated carbon. The potential benefits of activated carbon are great enough that on whole you will be better off using it. If trace element depletion is a worry, use a trace element supplement in conjunction with the activated carbon.

GAC cannot be rejuvenated outside a laboratory, but fortunately, it is cheap enough to use liberally. Always wash your carbon before use to remove the dust that accumulates during shipment. Advice on how much to use vary, but smaller amounts changed more frequently seem to work best. You probably want to experiment, but 1/2 cup per 20 gallons water, changed monthly is a good starting point. In summary, activated carbon is an excellent, cheap and effective filtration method which is highly recommended for all aquaria.

A variety of special chemical filtration media have been developed to remove specific chemicals. A common one is made from the zeolite clay (also used as some cat litters), and is marketed under such brand names as ``Ammo-Carb''. This media removes ammonia from water, and is good for short term use. The aquarist should be aware that if zeolite is used, especially when cycling a new aquarium, then the establishment of natural biological filtration will be delayed or disrupted.

Protein skimmers are primarily used in saltwater aquaria, especially reefs. They have the remarkable ability to remove dissolved organic wastes before they decompose. The process involves taking advantage of the polar nature of the organic molecules, which are attracted to the surface of air bubbles injected into a column of water. The resultant foam is skimmed off and discarded.