enviromental changes are commonly over looked when our plants trun south over night. make yourself a check list if your plant goes south check these things first before diving into your ph. even the simplest things of you leaving a fan on or off to long could change the temps and cause your plant to turn south. so do your best to keep the enviromental chages to a minimum and you will be rewarded with happy plants. YES I REALLY DONT AND NEVER HAD CHECKED MY PH OR E.C..
my feelings are if you try to mess with the water by adding chemicals you can over do it and do more harm than good. i would recommend if you want to lower your ph use a natural buffer like peat moss.peat moss you can just stuff in a pair of panty hose and toss it in the bucket and will lower the ph naturallly and stablize it. chemicals tend to be hard to get exact and everytime you do a water change you are not at the same ph and again it all falls back to keeping the stable enviroment! i can not stress it enought stable enviroment.
ever wonder why you plant wilts a little when you go from vegging under cfl's to flowering under 1000hps...its all the stable enviroment. i will actual begin to heat my veg area to match the flower room for less stress on the plant when it moves to the hotter room