That pH buffer system works, but it'll have a hard time doin' the work if it's having to even out after something with extreme pH is introduced.

I don't see why people are believing that pH up & down kill microbes, other than the fact any pH change kills at least some microbes (due to their specialized nature).

Whether you're using a pinch of pool pH stuff (soda ash and the like), or vinegar + lime to pH a solution it'll be a drastic change in pH that could kill microbes.

Granted, most stuff like EWC tea should stick within the safe range on it's own.