IF you are regularly having the chlorine get to zero, it sounds like you don't have the SWG on-time set high enough or that your weather is varying and you have it set to handle semi-cloudy days but not sunny ones. You should probably run your SWG longer and with a higher FC target until you get the hang of things in terms of what SWG on-time is needed to maintain the minimum FC. So target higher until you figure out how not to go below the minimum. Note that if you do not run the pump at all at night, that you need to target higher than 4 ppm FC at the end of the day so that there is still 4 ppm FC the next morning when the pump comes on. Basically, you should test your FC in the morning before the pump comes on since that should be the lowest FC level of the day if you are only running the pump during the day.
Your Hayward Goldline T-CELL-15 Turbo SWG outputs 1.47 pounds of chlorine per day which in 35,000 gallons is 5 ppm FC per day or [EDIT] 0.21 [END-EDIT] ppm FC per hour. That [EDIT] is woefully inadequate for your size of pool [END-EDIT]. What is your pump currently on and what is your SWG % on-time setting?
Your Hayward Goldline T-CELL-15 Turbo SWG outputs 1.47 pounds of chlorine per day which in 35,000 gallons is 5 ppm FC per day or [EDIT] 0.21 [END-EDIT] ppm FC per hour. That [EDIT] is woefully inadequate for your size of pool [END-EDIT]. What is your pump currently on and what is your SWG % on-time setting?