How long are you running your SWG per day? And what is the water temperature?
Once the UV load and water temperature are low, it just needs a few days of running the SWG on "summer settings" to get your FC up.
In winter, I don't have to add more than 0.5ppm with my SWG per day, less than 2 hours at 40%.
How are you measuring your pH? A drop test will read falsely high above FC 10. A pH meter reading would still be correct (I assume you have a pH meter to get a reading of 8.5?)
While producing more chlorine than you are using, your pH can rise. Once you consume more chlorine than you are producing per day, pH will move down again and reach normal levels (assuming you have no significant pH rise due to CO2 out-gassing with TA of 65) once FC is back to normal - that's when the chlorination cycle will be closed.
Let's say you started at FC 5 and pH 7.8. Chlorine production with your SWG to raise FC by 7ppm to reach 12ppm will bring pH to about 8.4. Chlorine breakdown by 7ppm will bring pH back down to 7.8 (calculated with Chem geek's PoolEquations spreadsheet).
So, pH can be higher than normal until the extra chlorine has been consumed.
