How does an API work and how it can help ports? Top API Architectural Styles API and API testing Eraser: API Diagrams. The API FRESHWATER MASTER TEST KIT measures the 4 most important levels in freshwater aquariums quickly and accurately, including pH, high range pH, ammonia, nitrite, and nitrate. With scientific accuracy for professional results, the reusable FRESHWATER MASTER TEST KIT comes with 4 glass test tubes with snap tight caps and a convenient holding tub for easy storage. Also includes a step by step instruction 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! See attached instruction manual for directions.