At elevated FC levels, the sun is going to burn through a lot. But it needs to stay elevated in order to eradicate any algae. Test as often as you can, no more often than once per hour, and raise FC to the SLAM level as often as you can.
I think I'm getting close. Only loss 1.3 chlorine last night and cc down to 0.5. But surely used some chlorine yesterday. Used 17.3 ppm yesterday during sunlight. That's not cheap just to watch it disappear.