Nutrafin pH Low Range Reagent Refill for Aquarium, 18ml Nutrafin ph low range reagent refill is for use with the nutrafin ph low range (6.0 - 7.6) test kit Ph levels should be monitored regularly as they have a direct effect on the well being and health of the fish Measures 1-inch length by 1-inch width by 3-inch height Comes in 18-milliliter refill pack