Keep your pH between 7.4 and 7.6 for a plaster pool.

That’s the sweet spot. Too low and the water etches the plaster. Too high and you get scaling. Everything else starts from there.

Balance alkalinity first (80–120 ppm) because it buffers pH. Then adjust pH. After that, test calcium hardness. For plaster, you want 200–400 ppm. Below 200, the water pulls calcium from your plaster. Above 400, you get cloudy water and deposits. Cyanuric acid (stabilizer) should be 30–50 ppm if you use chlorine tabs.

Test weekly. Adjust slowly — don’t dump in chemicals all at once. A little muriatic acid or baking soda goes a long way.

Plaster is porous and expensive. Keep it simple: pH and calcium are your two most important numbers.