Crosby,
Newly plastered pools (less than 30 days) have completely different needs than when the plaster has been under water for at least one month. Keep that in mind as I offer suggestions for you to follow for the first month of your new pool.
Since your plaster is less than 30 days old, the pH will always be very difficult to keep under 8.3. That is just the way it is. Fortunately, there is one way to ease that difficulty, and that is by maintaining the CSI (or LSI) at about +0.4 to +0.5 for 20 to 30 days. To achieve that high CSI, it is best to have a high alkalinity if possible, and the pH between 7.8 and 8.3. The calcium hardness should never be adjusted upward (if needed) until the pH is under 8.0. Daily additions of small amounts of acid will probably be needed for the first two to three weeks.
The following is an explanation about the above program, and it only applies to new plaster, not a plaster pool that is beyond 30 days. If or when the pH is low and/or the alkalinity is low, and the CSI is below +0.4, some plaster material (calcium hydroxide) will dissolve into the pool water and immediately cause the pH to rise dramatically. That is exactly why the pH in your pool water was tested at 8.7 (if I read that above correctly). Only by maintaining the CSI at a high level will prevent the dissolution of calcium hydroxide from the plaster surface. Once 30 days have past, there is no longer any calcium hydroxide on the plaster surface because it has been carbonated. It is no longer a problem to deal with. I have proven the above information through many experiments.
One other point, do not use liquid chlorine for the first month unless you add acid at the same time. Liquid chlorine has a very high pH and could cause scaling when added if not neutralized by adding acid at the same time and brushing afterwards to remove scale (if present) and to circulate the water.
My suggestion to you right now is to add acid and bicarb at the same time to lower the pH. If you add 7 lbs. of bicarb for every gallon of 31.45% acid, that will negate any change to the TA. But it will lower the pH. I would proceed to get the CSI to a higher level mentioned above. Brushing is always necessary and vital for new plaster pools. Thousands of pools are successfully using the Bicarb Startup program or the Orenda's Positive LSI Calcium startup program.
Once your pool is beyond 30 days, maintaining the CSI near the 0.0 level, and maintaining a low TA will help ease the constant pH rise and have to add acid constantly. Of course, the concept of using carbon dioxide is a good choice for pH control, but only when the alkalinity has been lowered.
If anyone sees something that I missed or has questions, please respond. Thanks.