(6 Pack) Dogit Replacement Filter Cartridge for Fresh & Clear Large Dog Fountain 18 total replacement dog fountain filter cartridges Designed for use with small or large Dogit Drinking Fountain Dual-function filters remove debris, food, and sediment from your dog's water bowl They also help reduce bad tastes, odors and absorb impurities from your tap water Filters should be replaced every 3 weeks or when the filter becomes visibly saturated with foreign matter