The Bluelab� hand held pH pen provides a compact quick and handy way to manage the success of your crop to ensure maximum uptake of nutrients. The Bluelab� pH Pen also measures the temperature of the solution, as root health is vital to the success of a crop. Temperature affects the growth rate and structure of a plant so a solution temperature of 18 - 22?C is recommended. Plants get their nutrient from minerals but they can only get all the right minerals they need if certain conditions are right. Think of nutrients like a lock. pH is the key. A key factor that affects food uptake is whether your solution is acid or alkaline. We measure this in pH. The Bluelab� hand held pH pen is the ultimate handy solution for measuring pH and temperature!