Abstract: There is provided a spectrophotometric system and method for measuring the concentration of discrete water-soluble compounds or minerals in the water of a live aquaculture basin. The system comprises a portable wireless spectrophotometer with an optical code reader for automatic identification of water sample cuvettes. The cuvettes bear an optical code identifier and are preloaded with at least one solid color indicating reagent dry tablet. The cuvettes are internally sized and shaped for a smaller tablet type to fall to the bottom and a larger tablet type not to not fall to the bottom and vertically rest at an intermediate height within the cuvette interior thereby creating vertical separation between the tablet types and avoiding cross-reactions or degradation while in storage or transport. The system can also include a mobile application for displaying the spectra results and for providing recommendations or e-commerce purchase means for water quality improvement.