I've look through the Pool Water Chemistry post and I have not found what I'm looking for. Is there a closed form equation (or even an interpolated equation or regression analysis) that describes the chlorine loss rate as function of FC level (and any other relevant water parameters such as pH, CYA, etc) where there is no UV exposure and no known loss due to disinfection or oxidation?
The reason I ask is this - for an OCLT where you're just checking to see if you have a problem, I have seen any number of different variations of recommended FC levels. Some have recommended that an OCLT really only tells you something if your at shock levels (one of the exit criteria for a SLAM), others say to do an OCLT at whatever FC level your water happens to be at when nightfall comes (this is the actual TFP Pool School method) and I've seen others recommend raising the FC up to 10ppm at sundown and then checking again in the morning.
So my question/inquiry is just to get a feeling for what the loss would be for a given FC level assuming the ideal state that you have no sunlight and no contamination in the water (organics or biological). Perhaps it's so low that it doesn't matter or would not be detectable by FAS-DPD testing, but I just have not found it yet.