Nutrafin General Hardness (GH) Reagent Refill for Aquarium for Aquarium, 10ml General hardness (gh) reagent refill for use with nutrafin carbonate and general hardness test kit Testing for general hardness (gh) should be done to determine if the levels of calcium and magnesium are optimal for specific species of fish Measures 1-inch length by 1-inch width by 3-inch height Comes in 10-milliliter refill pack