I just opened my 18,000 gallon pool and shocked with 4 gallons of liquid chlorine. FC was 1ppm and CC was 6ppm. Pool store said to add 18lbs of oxysheen. Now my FAS/DPD test is showing 14ppm FC. But my OTO test is still showing 1ppm. Does oxysheen cause the FAS/DPD test to show high FC levels? Do I need to shock my pool with liquid chlorine again?