I used to use vinegar, but i think it caused me algae white slime problems, so I switched to TopFin fish tank ph up and down... I did that for a week or so, and finally realized that it's just better for the plants to get something that is actually meant for the application that we use it for.
So I now use General Hydroponics PH down. and I have a huge shopping list of other stuff that I need, including PH UP, and AN barricade, and some other chemical buffers that I never knew I needed.
eeesh, complex stuff this hydro!