How can I avoid a pH crash?

[chem geek]

If your typical daily chlorine demand is 2 ppm FC per day, then in 12,000 gallons that would be about 9 3" 8-ounce Trichlor pucks/tabs. Starting out at 7.8 pH and 80 ppm TA you would end up at the same TA but with CYA higher by 25 ppm (adjusted TA or carbonate alkalinity would be lower by 10 ppm) and the pH would be no lower than 7.0 and with carbon dioxide outgassing will probably be more like 7.2 so you should be OK.