What is the pH of your fill water? I know that curing plaster will cause constant rising of pH, and I also know that many pools have a pH that they tend to stabilize at (mine will go to 7.8 and stay there if I don't do something to change it, and my efforts at changing it are pretty much just a waste of time and money!).

Since you have no CYA right now, you might want to consider chlorinating with trichlor for awhile since it tends to drive pH downward, and see if that helps?

Janet