Abstract: A fluid treatment apparatus (100) and method having a variety of interchangeable input/output cards (10) capable of communicating with a variety of parameters including analytical parameters. A programmable central processing unit (124), input/output cards (10), data bus (30), display (102), and keypad (104) are integrated into a single integrated apparatus (100). Analytical parameters are received directly by the appropriate input/output cards for direct communication with the central processing unit (124). The central processing unit also outputs control parameters through the input/output cards.