I've read all over these forums about this and still can't come to a conclusion. My water has been sparkling clear for weeks, and I've never let the FC level drop below 6 ppm, and CC has always been 0. CYA is steady at 50 (prior to rain, will test again tomorrow) Last night FC was at 8, and I added enough cal-hypo to bring it to 11. After the huge thunderstorm, this morning the pool was about 1/2 inch from overflowing, and the water was cloudy and light green. FC tested at 8, CC is 0. I added cal hypo to bring it to shock level of 16 at 12 pm. At 7:30 pm, FC was 11. Added enough cal hypo to raise FC to 19 and will test again in a couple hours to see if it is dropping. I put the filter on waste to lower the water level and vacuumed out a lot of detritus. The polaris got a ton of leaves off the bottom.
At any rate, there seems to be a connection between thunderstorms with heavy rain and pool water turning light green and cloudy. Maybe the addition of all of the organics from rain and water running into the pool just overwhelms the chlorine...however, wouldn't the FC be depleted if there was enough algae in the water to make it green?