@markphin: I am about 5 weeks post a re-plaster with krystalkrete. For the first 3-4 weeks, I was adding a similar amount of muriatic acid as you were. I was brushing the surface twice a day; however, a lot of the plaster dust was staying in the deep end near the main drain. Once I hit the 30 day mark and used my pool vac, I was able to vacuum any excess plaster dust. Since removing the plaster dust, the pH has stabilized. While the plaster continues to cure over the next 6 months, I still expect the pH to slightly fluctuate.

Make sure to test your water regularly.

Have you seen your pH stabilize? I realize this thread is almost a year old.