Benzelsanswered grow question 3 years ago Do a test. make up a small batch of your nute mix in a clean container...and just leave it. Test the ph each day and see what happens. If its just sitting around and not even being used on a plant, and the ph is changing daily, id look at a diff nute line, and good advice about letting water sit for 24 hrs or longer if poss if your not using filtered or RO water. Tap water is full of junk that should be given time to evaporate out if possible.
Also can try making up nute mix the day before you need it, dont ph it then, let it sit til the next day and then ph it then before use. Should also be a way to stablize it.