CH of my fill water is 120ppm, I tested it this morning. I think a aprtial drain will be worth the effort. Since I won't be dealing with the added complication of new plaster, dropping TA after re-fill should be a litte easier, right?

5.5 more cups of muriatic last night, TA down to 110 (uncorrected for CYA). I may have finally broken the plateau. Beating on it again this evening. The waterfall really helps with aeration, It brought me from a pH of 7.0 to 7.3 in about 2.5 hrs last night, running full pressure.