Does PH down solution keep the PH down for extended periods of time?

I have same issue. Vinegar won't do much. And phosphoric acid pH down leads to other nutrient locks. I found that pH will go down once plants develops. Plant produces citric acid at root tips. The issues is more complex than simple chemistry. Microbes in soil and how root interact with microbe influences pH. What works for me to lower pH are: Granule humic acid. Adding citric acid to water. Sitmulate root with sea weed. Adding yogurt with living microbe once. (1 part yogurt to 20 parts water.

If you pump air to the water it will raise your ph quick. It will stabilize at a certain point. At that point you will be able to mix and ph your water and it should stay pretty stable after that. If it's a rez though your ph will always change a little depending on what your plants are doing, drinking or eating. Cheers

The ions in the water react to the acid and raise the ph. Can't be helped unless you use deionised water. good luck and happy growing