If you're growing in soil and want to grow organic, lemon juice
or citric
acid powder both work well for adjusting water ph. In my case, we're on a well and my tap water is on the soft side (50 ppm) with a ph in the high 6's. Once I add
calmag to up the ppm of dissolved solids to an ideal range (around 150-200 ppm) it's up to around 7. 1 teaspoon of lemon juice per quart of water takes it down to around 6 for me, but different waters can behave differently depending on the types of dissolved solids so be sure to use a ph test kit to ensure you've got your water where you want it. Also, be sure to add the lemon juice
or citric
acid powder last if you're adding liquid nutes like nitrogen
or calmag to your water since some nutes can change the ph of the solution. I've never grown hydro so I can't comment on it's effectiveness in that medium.