Placement in Filter Activated carbon will lose its effectiveness rather quickly if exposed to lots of debris from the aquarium. Therefore, carbon should be placed after the mechanical filtration media in the filter. Keep in mind that if you do not keep your tank clean, and debris builds up in the filter, the activated carbon will not be effective.Changing Activated Carbon Since activated carbon binds with the compounds it removes, it eventually becomes saturated and can no longer remove additional contaminants. Therefore, it must be regularly replaced—once per month is usually sufficient. Longer intervals between replacements will not harm the tank, but the carbon will gradually lose its ability to remove toxins from the water. If you see yellowing in the water or smell an odor in your tank, it’s past time to change the activated carbon.
