Advice please

I've got seeds germinating. I mixed up some soil: 60% potting soil, 20% perlite, 20% sphagnum peat moss, and a liitle dolomite lime to buffer. I'm experimenting with adjusting water Ph. The guy at the nursery sold me dusting sulphur when I asked for stuff to lower soil Ph. He quickly put it in a plastic bag so I couldn't even see it. Anyway I added 4 heaping tbsp. of the sulphur to my water (2 Qt. pitcher) and the pH didn't budge. So I emptied the pitcher, added water, and put in 1/3 cup of vinegar and the ph read 6.0. So I'm figuring I'll try 1/4 cup to 2 qt. of water and try to get that 6.8 or 6.9. My question is it okay to adjust ph of water with vinegar? The sulphur might work in the soil but doesn't do much in water.

I remember a fella using vinegar on accident to feed a mother plant and she died. Every since then I have a little prejudice against it.
Adieu