Add acid, but expect to work for it.

You can lower pH with muriatic acid (or dry acid), but that high TA (180+) will fight you the whole way. Each dose of acid will drop pH temporarily, then it’ll creep back up as the alkalinity buffers it. You’re not just fighting pH — you’re fighting the buffer.

The real fix is to lower the TA first. Add acid to bring pH down to about 7.0–7.2, then aerate the heck out of the pool (run waterfalls, point return jets up, use a submersible pump to break the surface). Aeration drives off carbon dioxide, which raises pH but lowers TA. Repeat this cycle — acid, aerate, test — until TA drops to 80–120 ppm. Then you can fine-tune pH normally.

Expect several rounds. It’s tedious but works. And please: add acid slowly, in small doses, and never more than the label says at once. Test between each dose. High TA pools are stubborn, not unmanageable.