Nitrates are nitrogen compounds that occur naturally in the soil, but also enter the soil as a component of fertilizers. Even a small amount of nitrate in drinking water can pose a health risk! Sigrist ColorPlus 3 offers you online measurement of nitrate. As a light source, a long-lived xenon flash lamp is used having a very low loss of intensity over a long time! The medium is measured with two optical path lengths from which any soiling is determined. The value measured is automatically corrected and the instrument informs the user when the measuring cell has to be cleaned. The PVC cover can be removed without tools. Free access to the optics allows simple cleaning of the measuring cell. The instrument indicates any maintenance due. The control unit SICON selectively displays values, graphs, status and alarms on state-of-the-art touchscreen technology and colour display. Internal data storage allows the visualization of the measurements over the last 32 days. The instrument is used in the treatment of drinking water.