API REEF MASTER TEST KIT allows you to measure the 4 key parameters - calcium, carbonate hardness, phosphate, and nitrate - to keep reef populations healthy. The tests are quick, simple and accurate and provide precise results. The kit includes 4 glass test tubes with quick-release caps and a convenient tray for easy, reusable storage. This kit also includes a complete step-by-step instruction booklet with a color chart that provides information on how to remedy water quality problems.