The instrument is only as accurate as the probe is clean. Probe cleaning is one of the most important parts of owning or operating any Bluelab meter, monitor or controller. The probe surface is where the instrument takes the reading of the solution. If the probe face is dirty or contaminated, then the reading will be inaccurate. Accurate readings simplify crop management and provide improved growth. To re-stock your conductivity probe care kit, Bluelab 2.77 EC Conductivity Standard Solution is available in 20ml sachets, and 250ml and 500ml bottles.