I had to lower the P.H. of water yesterday as it was 8.5. In 4 litres of water I tried using 1ml of P.H. down and was way too much, Took it down to 4. After 2 more goes I got it just right. I only used 3 drops from the end of a syringe. This was the first time I have used P.H. down. So, if any other newbies have to bring down the P.H., only a couple of drops in 4 litres.. What annoyed me more was that there wasn't any instructions on the product, Growth Technology. It said they were on their website but nothing about P.H. down.
in my experience, I had way more issues with Ph curling, twisting, and burns when I used chemical ferts and adjusted Water's ph with meters and ph up and down. Once I stopped using Ph meters, all those bottles, and started tending to the soil food web, Well I haven't had any issues with that since.
Different pH up/down have different concentrations. You just have to use a few drops at a time to see how concentrated it is. Also, you need to wait about 20 min after using ph up or down, to let the pH settle and give you an accurate readout.