I have a 21,000 gallon in-ground pebble-tec combination pool/spa in hot central California, open year-round uncovered, that is 4 yrs old and has been managed since day 1 with unstabilized liquid chlorine. I've never had a non-clear day and overall have had very good balanced water. I constantly struggle though with a battle between pH and total alkalinity, every 10-14 days the pH creeps up to 7.8 at which point I add half a gallon of acid and it goes down to 7.2 or so, and slowly creeps up. In addition, the total alkalinity seems to want to live at around 60...I add baking soda every 2-3 weeks and can get it up to my target of 80 but this makes the pH go up faster to the 7.8 level at which point I have to add acid...so it's a constant see-saw between adding acid and adding base. I've got to the point where I'm ready to stop worrying about total alkalinity being at 80 and just leaving it at 50-60, and just keeping the pH in the normal range with a little acid every couple weeks.
Any thoughts or suggestions on this? My other levels are within normal limits. This is the original water in this pool.