Using the Catit Magic Blue Refill Filter Pads is super easy. First, make sure you have the Catit Magic Blue Cartridge (sold separately). Then, simply place the refill pads inside the cartridge. This setup should be placed in your cat's litter box. As your cat uses the litter box, the pads will start working to reduce ammonia and fecal odors. Remember, you get 6 pads in a pack, which is enough for about 3 months. Once you notice a decrease in odor - reducing performance, it's time to replace the pads. To keep your cat's environment healthy, always store the pads in a cool, dry place. And don't worry about any toxic substances as these pads are non - toxic and made of BPA - Free materials.