Imagine you have two identical pools, side by side. Same volume, equipment, water chemistry, exposure to dust/pollen, etc.
Both pools circulate overnight. FAS/DPD testing shows 3 ppm FC with no CC first thing in the am. CYA is 25 ppm.
Pool A is allowed to circulate throughout the day. Pool B has the pump turned off, so it is sitting stagnant in the sun.
Later that evening Pool B is turned back on and allowed to thoroughly circulate and mix, then both pools are FAS/DPD tested again.
What would you expect to find?
Pool A has thoroughly mixed water throughout the day, possibly allowing minimal CC to briefly form. However due to circulation, the deeper "protected" water is mixed and brought to the surface throughout the day.
Pool B, by sitting stagnant, had the top layer of water exposed to more sunlight, probably more CC created but the underlying water that was "protected" was, well, protected
What do you think the outcome would be of the testing at night?