WHEN SHOULD YOU REPLACE YOUR POLY-FILTER ?
When the POLY-FILTER turns DARK in color, it is still operating effectively and does not have to be replaced. However, when it begins to turn brownish in color, it should be removed, discarded and immediately replaced with a new POLY-FILTER.
In those situations where the POLY-FILTER has been subjected to heavy waste product loads for prolonged periods; i.e. ammonia levels ranging from 0.50-1.50 parts per million or higher, and the aquarium water continues to appear yellowish-green in color or cloudy in appearance, then the filter is no longer effective and should be discarded and replaced
immediately with a new POLY-FILTER.