Something is causing high demand for chlorine. My pool is about 15,000 gallons, vinyl liner. CYA is 30; TH is 250; PH 7.4; Alkalinity 120; TC 1; FC 0. Those readings were taken in the morning - 12 hours after adding 6 lbs. of cal hypo chlorine the evening before with the filter running continuously overnight. The water is clear, no sign whatsoever of algae. What's my next step? Should I try 10 lbs. tonight to break the "lock"?