About Activated Carbon
"Another common concern when using carbon efficiently is that it will quickly strip the water of desirable trace elements.
Although this warning is repeated with regularity in aquarium literature, this consequence of carbon use has never been scientifically demonstrated to occur.
Efficient carbon use has also been implicated in causing head and lateral line erosion (HLLE
) syndrome in certain fish (marine angels and tangs, and freshwater discus). This "cause and effect" relationship has also not been demonstrated scientifically."
"The next logical question is how often to replace the carbon. There is a test kit now available from Salifert that measures the adsorptive capacity of the remaining carbon. This simple test is a good method for determining a replacement regimen. Another frequently suggested method is to place a white plastic card in the aquarium and observe it through the long end of the aquarium. If it has a yellow tint, that's an indication that the carbon has lost its effectiveness. You can also draw a faint yellow line on that card. If you can't discern the yellow from the white when viewed through the long end of the aquarium, that's also an indication that the water has yellowed and the carbon has lost its effectiveness.
Carbon can lose a large percentage of its effectiveness in two to four weeks because organic material and bacterial slime coat the surface of the grains.
This effectively blocks access to the inner pores. The coating can be rinsed clean between carbon changes as a means of extending the useful life of the carbon