Question for the more knowledgeable folks here.

I've put in about a gallon and a half of muriatic acid over the past several days, and can't seem to keep the pH down to 7.2 or below, yet the TA doesn't seem to be dropping that much yet. TA appears to want to hover for a while at the high levels, even with the spray rig I made. I realize the instructions said it will take a while, but shouldn't I have been seeing a more pronounced drop already? I'll test again tonight, and see where it is.