Finest-Filters Oase Biotec 5/10/30 Replacement Filter Foam Set (6 x Blue Coarse and 6 x Red Fine Foams) You are purchasing 6 x compatible replacement coarse foams and 6 x compatible fine foams to fit the Oase Biotec 5/10/30 pond filter. Our replacement foam filters are made from high quality reticulated foam, in the same specification and colour as the Oase original filters. The size of these foams is approx 25cm x 25cm x 8cm. They have a slit through the centre. Please Note: This is NOT a genuine Oase original filter, it is a Finest-Filters alternative which performs the same job.