Running with un-controlled chlorine levels (no testing) can DEFINITELY get you in trouble. Sounds like you may have ID'd the problem.

@Carl: I called Hoffinger, and talked to several people there. Apparently, they even do their own molding for the plastics in the pumps and filters. They do buy the resins and raw PVC, but in rail cars. At that level of ops, I would assume they do QC analysis on the incoming raw materials.