How to reduce acidity

I don't really follow F1/F2 pattern but just get out some into a jug and re-top the rest with tea.

That worked for me for some time, but now it doesn't - kombucha I have is often too sour for my taste. And I'm not really sure why. Also I'd like it to be a bit sour but minimize vinegar "burn".

Are there any tips for reducing sourness?