WHAT YOU GET4 sets of cat fountain filters. Each set includes 2 sponge foam filters, 1 activated carbon filter. Stronger filter capacity, 4 sets, can be used for 2-4 months. Compared to other cat fountains which 1 set only has one filter, our cat fountain filter system is more powerful! COMPATIBILITYOur filters are designed for our WF150 model cat fountain. Please make sure your cat water fountain model and check the size before purchasing. MULTIPLE FILTER SYSTEMOur filters were combined with 2 high density sponge foams and 1 activated carbon and ionic resin filter, it was covered with high quality natural fleece, durable cotton layers, the foam layers sponge and resin can absorb hair and coarse dirt, and activated carbon can eliminate odors in water. Clean, fresh water always available! FILTER REPLACEMENT FREQUENCY To ensure the water quality and taste, please change the filter every 2-4 weeks, before using the new filter, please soak the filters in the water for 2 minutes to prevent activated carbon dust from entering the water. HEALTHY LIFECat likes to drink running water, fresh and clean water will make cats healthy and strong, healthy cats, happy owner!