subject: Why Freshwater Filters Cannot Be Used In A Saltwater Aquarium [print this page] Freshwater and saltwater filters function differently and the difference is because of the sensitivity of the fish.Freshwater fish are generally able to withstand harsher conditions. Out in their natural environment, the space that they live in is generally not large and therefore experiences constant changes in chemical concentration and temperature. This has caused them to be hardier and able to live in conditions that are less stable.
The filters used in freshwater aquariums perform mechanical, biological and chemical filtration. Porous filter media takes care of mechanical filtration in which water is forced through the filter media which traps large sediments and matter such as uneaten food and waste and is then poured back into the aquarium cleaned. In biological filters, colonies of beneficial bacteria are used to reduce large organic waste into matter that is less complex and less harmful which is then removed from the water by changing the water regularly. Chemical filtration uses material such as activated carbon to get rid of chemicals such as those used in treating disease from the tank water.
While they are work well for a freshwater fish tank, the fact is that the waste products are still in contact with the water supply until the filter media is cleaned or the water changed. As long as is happening, pH and chemical levels will constantly fluctuate which is detrimental to saltwater fish.
Saltwater fish live in the vast ocean where these conditions do not fluctuate within a large radius. Because of this, they are naturally not resistant to change. Therefore the environment that you create in your aquarium has to be as consistent and stable as the environment from which they came from. Waste needs to be removed immediately and there must be little or no trace of chemicals.
Protein skimming is an ideal mechanical filter because it removes organic waste from the water without giving it an opportunity to be reduced into lesser components such as ammonia which is harmful to the fish. This immediate removal will cause no reaction in the water and therefore no fluctuations in chemical and pH levels. This form of mechanical filtration bonds bubbles to the waste matter, which is them brought to the surface in the skimmer's column and is then ready to be discarded in the collection cup. All you then need to do is empty the collection cup from time to time and the water remains pristine. This method of filtration also removes the need to change water a lot.
However, even with protein skimming, nitrate will still build eventually. This is where live rock and live sand come into play. These natural biological filters reduce ammonia into nitrite, then nitrite into nitrate and finally nitrate into nitrogen gas. This is different from the biological filters in freshwater fish tanks that break waste matter into nitrate as a waste product that still needs water changes to remove them. The nitrogen gas that is produced is harmless and will escape the fish tank water naturally into the atmosphere outside.
The combination of protein skimming, live rock and live sand create an environment within the saltwater fish tank that is very stable and requires almost no intervention from outside. Thus the saltwater fish which are more sensitive are allowed to live in a condition which is the same as the one they originated from.
