These types of products are designed to "absorb" chemical or natural compounds, toxic contaminates, medications and other unwanted elements in water, but they only do so up to their "absorption capacity". Once they have reached their absorption limitations they become exhausted, meaning they have reached the maximum amount they can absorb. Once this occurs the product ceases to work and the undesirable element(s) it has been removing bypasses the removal process, and thus remains and begins to accumlate in the system again.
It is important to read and follow the manufacturers instructions for using such products. Even though a few are designed to be cleaned or rejuvenated and reused, most DO need to be changed and periodically replaced. As far as how often depends on various factors:
- How a particular product works.
- How much is used.
- How heavy the saturation of a particular element such as phosphate or nitrate is in the aquarium water that needs to be removed.
Other considerations to keep in mind when using these types of products:
- Often they not only remove undesirable elements, but desirable ones as well. For this reason some manufacturers recommend that you remove or bypass their products when adding vitamins or replacing trace elements through organic bound solutions.
- Although these products are able to remove elements from the water you do not want, they are just band-aids. An aquarist should not rely on them as a permanent fix. Proper aquarium maintenance routines still need to be followed, and finding the "root" of a particular water quality issue and correcting it is important to prevent the perpetuation of the problem.
- By not changing or rinsing water prefiltering materials of most any type and allowing them to collect excessive amounts of detritus and other DOCs (Dissolved Organic Compounds), they become nitrate factories themselves.
