Odor Crystals -------- Remove even the strongest odors - like magic. These odor eliminators contain no perfumes or chemical cover-ups, just all-natural volcanic zeolite ingredients in crystal form. Hang a bag in any room odors are a problem, like near a litter box, and the room will soon be odor free. Renew each bag's odor-fighting power by placing in direct sunlight every 8 months. Large rooms or stronger odors may require more than one bag. Use one bag for every two pets in household.