Replacement calcium buffer for the Benchmark Calcium & Magnesium Test Kit. 118 mL bottle Contains 4% sodium hydroxide Add 1.00 mL to a 5.00 mL aquarium-water sample One replacement reagent only; indicator, titrant and testing tools are not included Use only as directed with the Benchmark Calcium Indicator and Calcium Titrant. Best value: Need every calcium and magnesium reagent? Choose the Calcium & Magnesium Refill Reagents. Need the tools too? Choose the complete test kit. Warning: Contains sodium hydroxide. May cause severe skin burns and eye damage. Wear suitable eye and hand protection, keep out of reach of children, and read the product label and SDS before use.