Dry acid (sodium bisulfate) works fine.

Use sodium bisulfate. It’s the standard alternative to muriatic acid for lowering pool pH, and it’s safer to handle. You can buy it at any pool store as a granular powder. Just follow the dosage on the bag—start with about 1 pound per 10,000 gallons to lower pH by 0.1–0.2, then retest.

Sodium bisulfate is less aggressive than muriatic acid, so you’re less likely to over-shoot or burn yourself. It does add sulfates to the water, but that’s rarely an issue unless you’re on a strict mineral-balance regimen.

Whatever you do, don’t use vinegar or lemon juice. You’d need gallons of the stuff, and the organic matter will feed algae. Stick to pool-grade chemicals.

Aim for 7.4–7.6, test weekly, and you’re set.