We use soft water (Hardness < 5 ppm) for our closed loop chilled water system with soft water make-up facility and Chemical Nalco R-39 M. We just change the water 45 days ago but suddenly today we find TDS: 450 PPM, pH: 8.81 & Hardness: 17 PPM. Is it good enough or we need to take any precaution? I try in the Google for any reference for closed loop chilled water system but did not get any authentic papers! So, if any body help me to find any reference.