Good to know the hardness or at least the ppm of the source water before adding acid. The ph is not always a good indicator.
I use 8.0 ph well water but it has only 150 ppm mineral content so it easily conforms to the medium ph and needs no adjustment.
agree 100% Alkalinity is important to know. You can buy. KH test kit from a pet store or see how much carbonate/bicarbonate is in your local water supply usually from the report.
RO water is stripped of all and should be reconstituted if your nutes don't do so.
I rely on the grow shop guys to steer me in the right direction with that stuff. I probably pay too much for the stuff but rely on the experts....right?....I have some brand named PH Up but my down is some stuff they mixed up themselves, no label wtfk's what they sold me but it works a drop at a time. They probably told me at the time what it was but I'm 67 add a few pipe fulls , a few months and well my memory is not what she used to be.
Your ph up is potassium bicarbonate dissolved in water.
You look at ph down read the ingredients... Look it up online you can find out what's in them. Most Ph down for hydro is 85% phosphoric acid. It's simply acid and distilled water and I'm betting that's exactly what they gave ya. I do agree if you don't understand it's safest bet with anything to use premixed packaged stuff. But I can tell you the info I have given is safe and accurate. If you buy 85% food grade phosphoric acid.... It's no different than any brand name phosphoric acid based ph down. Almost all ph up is potassium bicarbonate although I'm sure there are some with other carbonate and bicarbonate sources I just haven't looked to much into it.
I have been adjusting ph in water for aquariums, aquatics and now hydro for a total of over 25 years.