Ok to lower PH that is 7.6 or higher (mine is 7.6 exactly) based on a pool water PH Testing kit. (it's all I had and hell I am cheap hence why I started to grow my own this year)
So I wanted to lower this 7.6 water to 6.2 thru 6.5
like our plants need and love, I read here that plants will not be able to accept MOST of the nutrients your adding if you do not have your water PH at 6.5 ish
Basic rule is Vinegar to lower, baking soda to raise
(I happened to have about 3 fresh lemons (a Vinegar or acid, hell I guess even pickle juice would work too...) and I add just under 1 Teaspoon to every 1 liter of my 7.6 tap water.
I filled up a 5 ltr water jug and added about 4 Teaspoons and it was dialed in at 6.5ish.
I am sure that this will vary by whatever acid you use but I am pretty sure you can say it would be safe to say all lemons have the same acidity within a few .ph's I dunno.. maybe even oranges would do the same but at a maybe 2 teaspoons per ltr.