I'm betting that if the problems you have are nute related, it's the vinegar causing the problems.

I'm too lazy to go look it up, but isn't acetic acid gonna chelate to the acetate form?

Prob citric and tartaric in there too, depending on the brand...and who knows what else making up the other 95%. High sodium in most of the food-labeled stuff.

So you know, vinegar is sometimes used as a herbicide on OMRI cert corn fields- Corn'll take acetic at like 15-18%, but a foliar application of even the 5% you're using will kill just about all the common pest plants. Just sayin'.

I'd go the couple bucks and get some phosphoric- hell, get some GH pH- from the same place. It's phosphoric at a known concentration in nice clean reagant grade water- something you can work with...