Nothing wrong with it. Been using them for years.

If you use commercial nutrient solutions, they are buffered and Ph will not react much to vinegar and etc.

Ph up and Ph down are tailored to commercial nutrient solutions.

I suppose Willard and I will never see eye-to-eye on this one.{{gwi:996599}}
The problem a lot of people have with vinegar is that it "jumps back", meaning that - considering that vinegar is a weak acid - the pH goes down quickly, but comes back in a few hours. The reason is that the vinegar tends to replace the bicabonate content releasing CO2-gas which stays in solution for a while. So the pH goes down quickly, but - after a while as the CO2-gas gets lost - it goes up again.
What you need to do is stir virogously or . . instal a pump.