You can't lower pH quickly without chemicals.

You can’t. At least not quickly, and not without adding something acidic. pH is a measure of how acidic or basic your water is, and the only way to move it down is to introduce an acid.

“Aeration” gets mentioned a lot, but that actually raises pH by off-gassing carbon dioxide. Running a waterfall or fountain will make your pH go up, not down. So that’s backward.

Some people try vinegar or citric acid from the grocery store. Technically those are chemicals (everything is) and they’ll lower pH, but they’re weak acids. You need a lot, it gets expensive, and you risk clouding the water or feeding algae. Muriatic acid or sodium bisulfate is what works—those are the “chemicals” you’re trying to avoid.

If you really want zero pool store additives, your only option is to let it drift down naturally over days or weeks as rainwater and debris add acidity. That’s slow and unpredictable.

Get the acid. It’s the right tool.