ScoopFree Litter Tray Refills with Premium Blue Crystals ScoopFree Litter Tray Refills with Premium Blue Crystals Litter tray is completely disposable, so you don't have to see, touch, or smell messy waste Premium Blue Crystals litter immediately absorbs moisture and odor and dehydrates solid waste to stop odor. Recommended tray replacement: At least once every 20-30 days for one cat, 10-15 days for two cats, 7-10 days for three cats pre-filled with Premium Blue Crystals litter