The API® REEF MASTER TEST KIT test 4 key parameters – calcium, carbonate hardness, phosphate, and nitrate – to keep reef inhabitants healthy. Testing is fast, easy, and accurate, yielding precise results, and comes with 4 test tubes and a convenient holding tub for easy, reusable storage. This kit also includes a complete, step-by-step instructional booklet with a color chart that provides information on how to correct unsafe water conditions. We recommend that you take a few minutes each week to monitor your aquarium conditions and create a better underwater world for your fish. Testing your aquarium water has never been so easy or accurate! Sizes Contains 7 test solutions, easy-to-ready instructions, 4 test tubes and color chart Guide: See attached instruction manual. or visit API official website.