Any help would be great. Losing 4.5 ppm FC over past few says after losing 2.5 for first couple weeks. CYA 70. CC 0. PH 7.6. FC at 5.5 end of day til one gallon of bleach bumps to 10. Vinyl siding. 18 x 36. Approx 19500 gallons. Clear and no algae. Any suggestions or clues i could use?