A modular test system of individual reagents for professional users with a high frequency of tests. Liquid reagents are supplied in 30 mL and 60 mL dropper bottles which can be refilled. Reagents are available in pack sizes from 30 mL to 1000 mL (4.5 g to 75 g for powders). Currently 17 titrimetric and photometric methods are available within the aquaspex professional range.