A chemical measurement device for determining the concentration of given chemical in a given fluid has at least one LED light source and at least one light detector. The given chemical has a light absorption curve with a peak, and the at least one LED light source and at least one light detector are configured to collaborate to produce two light signals having peak wavelengths between about 5 nm and 35 nm apart. The two light signal peak wavelengths are in the ultraviolet region with wavelengths beyond the light absorption curve peak. The light signal peak wavelengths, however, also are before the light absorption curve is negligible. The device also has a concentration calculator operatively coupled with the at least one light detector. The concentration calculator is configured to compare the two light signals to produce a concentration signal representing the concentration of the given chemical in the given fluid.