Aqua Master Combo Pen P110 ProOverview The Combo Pen P110 Pro from Aqua Master features a modern design and heavy duty housing to prevent damage. This pen is ideal for measuring the EC, pH and temperature of your nutrient solution. The pen comes fully calibrated and includes batteries, so you can use it straight away. General Information One unit to measure EC, pH and water temperature. Unlike many others on the market, the Combo Pen P110 Pro is designed for dry storage, meaning