OASE Indoor Aquatics Pre-Filter Foam Set of 6 for The Biomaster 30 Ppi, BlackThe pre filter foam set 30 ppi for the biomaster 250, 350, or 600 includes six coarse replacement filter foams. The combination of coarse and fine filter foams allows you to customize to meet the filtration needs of your aquarium. Timing to replace the pre filter foam set varies upon aquarium size, number of fish and plants, and declines in filter performance. The Pre Filter Foam Set 30 Ppi For The Bio Master 250, 350, Or 600 Includes 6 Coarse