PH Question

I have a dozen plants growing DWC. But one of the buckets in my flower room has some crazy PH happening and I dont get it. It will fluctuate from anywhere in the range of 3.9-12. This is all while holding the tester in the res. None of my other plants do this and I use the same nutes in all plants in flower room. I have tried changing the res and even when I do it will stay normal for the night. The next day when I test it its all crazy all again. Anyone ever have this problem? And no its not the tester it is calibrated and shows correct readings in all other res's

take a sample in a glass of the nutrient solution from the Res. thats giving you problems.
and test it.

After you add Ph up or Down your supossed to wait like 20 minutes or so
before taking another reading.

If that doesn't help. ask your self whats differnt with that DWC set-up.
maybe some metal or something.

thick, slow dissolving ressidue on bucket? causing an occasional swirl like effect? is the bucket closest to something the others are not?

another thing that will screw with you is if you take a reading and it's to low and you haven't waited 20 30 mintes for the solutions Ph to stablize and you add Ph up, and then you take a reading and it's to high, and you add Ph down.
well any way you'll chase it until your nutrient solution is junk.

You should only need Ph Down.

If you start with Ph nuetral water when you mix your nutrient solution
your Ph should be right in range of where you wanna be.
If you use tap water that has chlorine or chlormide in it. then your gonna hve problems with your Ph.