Have you measured the pH? If the mix is truly too acidic how did that happen? Since it’s a container you have control over what goes into it. Did something go wrong? You could remove and replace the mix.

How acidic is it? I have a hard time understanding how that could happen as container potting soil is seldom acidic enough.

I once or twice a year water with some vinegar in the water

Vinegar wouldn’t make it more alkaline. The question is the opposite of what most people would be wanting. That’s why we’ve asked what the pH actually is.