OASE Prefilterfoam set 6 BioMaster 45ppi

The Pre-filter Foam Set 45 ppi for the BioMaster 250, 350, or 600 includes six fine replacement filter foams. The combination of coarse and fine filter foams allows you to customize to meet the filtration needs of your aquarium. It is best to replace the pre-filter foam when you notice a decline in aquarium filter performance.