Get the borax in there as soon as you verify the 6.2 PH add the entire box....I have never seen a number that low..it must have been really low BEFORE the guy added the acid. but you MUST raise that PH...

also pour the clorox in....your FC is very low....one gallon tonight....and one tomorrow night.
and you need to get some stabilizer in too...

hope you weren't paying this pool guy.....