I use 98% sulphuric acid and lab grade potassium hydroxide granules for PH. Industrial I know but I need milligrams of it. During flowering I add humic acid and fulvic, which are both reasonably acidic so the sulphuric is not often required. My reason for this is that it makes getting my res to the right PH a breeze. I know exactly how much I need to get it spot on and just weigh it all with the nutes. 5.8 is my target in both coco and dwc. I let it vary a bit more in dwc.