The main function of Chemical filters is different with common aquarium filters. It's not to prevent debris or filter out the aquarium dirt but intended to make the water quality of aquarium become as we want, for example with activated carbon media and peat (humus). Utilization of chemical filters will help us create an aquarium conditions similar to the original condition in which fish and plants life.
Activated carbon (charcoal) is usually used in aquarium for chemical filtration. In a new aquarium set up, the percentage of hazardous substances that exist in the water such as ammonia and nitrite are still very big. This is because the nitrogen cycle process (which takes four weeks) has not run. During this period, active carbon can be used to absorb the ammonia, nitrites and other harmful substances.
Activated carbon is capable of absorbing other hazardous substances; also slowly absorb trace elements needed for plant growth. But this is not a big problem, because during the critical period of aquarium (first month) the nutritional needs of aquatic plants are still very small. Thus the active carbon also serves to absorb excess nutrients in aquarium, so that algae growth can be inhibited. If the nitrogen cycle has been running, activated carbon can be removed and replaced with other filter media, e.g. bioball, to increase the biological filters capacity.
To increase the absorption of activated carbon can be done by selecting the activated carbon (charcoal) in small size. Because smaller particles of activated carbon have more surfaces. So the absorption is greater.
Good quality of activated carbon in addition to not change the pH levels, can also to absorb yellowish water, so the water becomes clearer.
Peat is usually used to 'soften the hardness of water' (eg for maintenance of Discus fish). When the water hardness level KH 3 �dH, then the peat media is not required. Peat is not popularized its use because it will make the water brownish (like the tea water.) Unlike wood that can also cause brown water, but still can be eliminated by frequently water replacement; the peat filter treatment was not practical at all.
Peat is not the aquarium fertilizer. Peat is humus used to reduce pH and water hardness level.
Reverse Osmosis (RO) is a tool to water purification or sterilize the water of all mineral elements so the hardness level is 0 (zero). Water with these conditions may not be suitable for fish. Therefore, trace elements should be added to make it suitable for aquariums. "RO water" is used for aquariums that require a high water quality and free of pollutant.
UV Filters or Ultraviolet filters effectively used to kills fish diseases bacteria so commonly used by fish suppliers for the ornamental fish they sell are not affected by the disease.
UV filters are also effective to eradicate the algae. However, these chemical filters are not suitable for aquascaping aquarium because it would also eliminate the trace elements needed by aquatic plants. UV filter is more commonly used to eradicate the alga that grows in the pond.
