API Saltwater Aquarium Master Test Kit It measures the 4 most important saltwater parameters pH, ammonia, nitrite, and nitrate to enable easy testing of your tanks natural cycle, and to aid in maintaining a thriving saltwater aquarium. Testing is fast, easy, and accurate, yielding precise results, and comes with 4 glass test tubes with snap-tight caps and a convenient holding tub for easy 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. it can conduct 550+ tests, so you can get the most out of your kit for years of fast, accurate water testing. Fill a test tube with 5ml of aquarium water. Hold bottle vertically & follow directions. Use for weekly monitoring and when water or fish problems appear Measures levels of calcium, carbonate, water hardness and phosphate