I've had a few algae blooms when using a solar cover even though the chlorine levels were at 7.5 to 8.5 ppm (CYA at 65, temps 80 degree). . now that the cover is off all the time no algae even though the chlorine is 4.5 to 5.5 (cya 50, temp 68 ish). Could the cover cause algae and what can I do about it?