Jim,

There are lots of options for selecting a chlorine monitoring system. The Hach CL-17 (800-227-4224) uses a DPD method for chlorine analysis, so there are bottles of chemicals to replace every month or so. There are a number of amperimetric electrode units also available from companies like ATI (800-959-0299), Great Lakes Instruments (414-355-3601), and Rosemount. These units have to be calibrated every 5-7 days (from our experience) and the electrode membranes replaced every few months. All of these options come equipped with alarm relays, require 120 VAC, use a small sidestream flow (about 1 lpm) that must be wasted, and cost between $2,500 - 3,500.

Another possibility is to use an ORP probe instead of a chlorine analyzer. You would have to run lab tests to correlate ORP levels in millivolts with chlorine levels in mg/L. Stranco (800-882-6466) sells a high-performance ORP monitoring system whose cost is similar to that of the chlorine analyzers. A cheaper system is available from Cole-Parmer (800-323-4340) for about $375 (see page 631 of their catalog). We have had mixed success trying to use ORP as an indicator of residual disinfectant. Each manufacturer's probe seems to respond differently and in general, they are slow to respond to step changes in chlorine levels. Most people in the water industry don't believe in using ORP to monitor chlorine levels.

Hope this helps.
Lew Rossman