The Ultra Monthly Monitor crystals contain pH indicators that help cat owners know if their cat is suffering from a common condition called FLUTD (Feline Lower Urinary Tract Disease). The monthly monitor works with all types of litter including clay, silica, corn, wheat, pine and paper. Once a month, cat owners pour monthly monitor screen on top of their newly changed litter box. Then after the cat urinates in the litter box, the pH indicators on the monthly monitor change color. The cat owner simply compares the color of the crystals at the pee spot to the colors on the tag included in each bag to determine an approximate pH range. To be accurate, this should be done as soon as the cat leaves the litter box (within 10 minutes). If the color indicates a urine pH in the low or high range, the cat owner should contact their feline veterinarian for advice on how to proceed. Cats usually don't show signs of being sick until their condition becomes serious. Cats with feline lower urinary tract disease (FLUTD) often go undiagnosed. FLUTD is most common in cats 3 years of age and older. Especially in male neutered cats as they get older. Urine pH is a reliable indicator of the health of the urinary tract. The Monthly Monitor with Health Indicator Crystals gives cat owners a way to monitor the pH of their cat's urine each month. Finding urine pH abnormalities early allows correction before FLUTD becomes serious. The incidence of FLUTD increases with age, so the older a consumer cat the greater the need for diagnostic litter additives. EASY TO FOLLOW INSTRUCTIONS The back of each sachet contains clear instructions on how the product should work and what to do if a low or high pH is indicated. The monthly observation is well received by cats because its sand-like texture is preferred by cats.