Measures pH up and down and conductivity level (TDS) in water to ensure plants get a balanced feed with lab quality glass probe; General uses include hydroponics, growing tent, swimming pool, drinking water, aquarium, fish tank, and brewing Double junction probe has a longer lifespan compared to standard probes and is more accurate than comparable pens, test strips, drops, and more; Different units available for conductivity (TDS, EC, PPM, and CF) Easy calibration for pH tester (Calibration optional for conductivity pen); Combine with meter and monitor for full garden nutrient monitoring in solution and soil Other features: Auto off function, low battery indicator, units for temperature; KIT INCLUDES: Batteries, calibration solution, probe care kit for pH and conductivity, Bluelab's Grow Book, and Grower's Wall Chart.