a fluid content monitor including a cuvette , a colorimeter adapted to generate a signal indicative of contents of a fluid sample contained in the cuvette , a container for holding a reagent , and a pump assembly for delivering reagent from the container to the cuvette . the pump assembly includes a tube extending from the container to the cuvette , check valves preventing reverse flow in the tube , and a hammer driven by a solenoid for repetitively compressing the tube to pump reagent to the cuvette . the cuvette can be removed for cleaning and replacement .