Ordinary household vinegar could in theory be used to lower the pH of your pool. The pH of vinegar is about 2.5, which is quite acidic when compared to your pool water. Household vinegar is very weak though (when compared to a strong acid like muriatic acid), so you would need quite a bit to lower pH.

Can you put vinegar in your pool?

Just like you run vinegar through your coffee pot to get rid of calcium buildup, white vinegar can wipe away this eyesore in your pool. ... It's OK if a little bit of it makes it into the pool water, but if you're concerned, test the water after using vinegar, and adjust any levels if necessary.

How do I lower the pH in my pool naturally?

You can lower the pH in your pool naturally by directing the downspouts from your house into the pool. If a pool becomes too full due to backwash it dumps water. Since rain is about 5.6 pH it is going to bring down the pH of the water naturally. The problem that you will have with rainwater is its low alkalinity.