Purchase a Milwaukee Digital EC Meter
This Milwaukee SM302 EC meter will help you to keep your nutrient level where it should be for proper feeding. You can keep from overfeeding your plants. EC is short for electro conductivity and can be thought of as the strength of your nutrient in the water. Most plants do well at 1.2 - 1.8. This meter comes in a protective plastic case. It also comes with solution for calibrating the meter. Batteries are included. It has a range of 0-10.0. It has a one year manufactures warranty.