The question was a mater of curiosity since we use 130 to 150 gallons of chlorine a year. Pool treatment system was originally Ozone with sand filter [which was removed due to wear on copper pipes to the boiler located 150 feet from pool) that corroded the 3 inch copper plumbing in the pool's mechanical room. It was change to a salt system, however, after 20 years rust appeared on one of the SS rails in the water for the steps and a landscape architect convenience that owner salt was causing the corrosion. The system was designed by a "pool engineer". We maintain a low Chlorine PPM since we pump 122 gallons a minute through the UV enclosure that has two 135 watt bulbs. The idea for the UV was to minimize the chlorine and we never had a problem with algae. Normally we maintain the system at .5 PPM chlorine, however, when we added calcium this fall, the BEC System raised the chlorine level and the FCL & CL is 1.59 at present, PH 7.4, ALY 126, CH 240, CY .4 and the TDS is 624 which gives a Langelier index of -0.08