Milwaukee PPM or EC meter
The Milwaukee Waterproof series of EC & TDS (PPM) pens allow you to monitor your nutrient solution for best plant growth. They all feature replaceable electrodes for long life. The batteries will last 1500 hours of use. The EC and TDS pens have automatic temperature compensation for accurate readings.
The TDS pen will measure from 0 to 2000 P.P.M. and the EC pen will measure from 0.00 to 10.00 EC. They have a 2 year warranty on the pen and 6 month warranty on the electrodePrice: $79.95