I'm closing my pool and bringing my chlorine level up to SLAM level. CYA is around 70 (SWG). I added three gallons of 12.5 chlorine and the pool got up to 22FC. So the next day, I put in another gallon and I only got about 2 more PPM. Weather is chilly, no one is swimming but it is sunny so I guess that could have taken some of the increase out of the total, but I'm wondering - at high CYA, does the addition of more chlorine have diminishing effects on the FC reading? According to pool math, I should have got around 7ppm out of the additional gallon. SWG is off so it wasn't adding an CL during this time.