Replacing filter foams is essential to help maintain a health, clean aquariums. There is no set rule for when your need to replace filter foams in aquarium filters, however, there a re many signs such as dirty water, poor water quality and reduction in flow from your filter that help indicate when this needs doing. Although a foam may may look fine in appearance, it may have shrunk over time allowing debris to pass this stage of the filter so its advised always having a spare handy to compare.
These foams are specifically designed to fit the BioMaster and BioMaster Thermo external filters. there are 2 foam grades to choose from, one fine to catch the finest particles and a more course foam for larger debris. These are colour coded, the fine being red and the course being blue. Each cut to shape to fit snugly into the filter compartment.