Why is my PH possessed?

I would double check the batteries in your PH meter, Also get some calibration powder and make sure its correct. It could of dried out and went out of wack Happy Growing.

Digital PH meters need some PPMs to figure stuff out. Straight RO water can’t be read and the meter will just drift because there’s nothing in the water to charge. These meters input a bit of an electrical charge to be able to figure put how the PH or PPM. Like other have said add a bit of cal mag to get some PPMs in there. I would also recalibrate your PH meter because by trying to read RO it may have thrown off the calibration. I stopped using RO because of these issues. Plus my tap water is around 55-60 PPM anyway so it’s low enough. Anyway good luck 🤙

Try adding some calmag to your RO water as the meters find it hard to stabilise in RO water. You should bring the EC up to 0.2-0.4 with calmag before adding nutrients, then adjust your pH and she should stay stable. I used deionised water for my first few grows and noticed the same thing. I used distilled vinegar as my pH down. Would adjust to pH 6 and the next day it would be climbing past 8. I only use tap water now as my water has <50ppm impurities. My water doesn't move from where I put it now. I hope this helps, good luck and happy growing

Vinegar (acetic acid) is not stable so it can adjust pH in the short term but it will soon rebound. Phosphoric acid is probably the most commonly used acid to adjust water pH though you can also use nitric acid but it is more difficult to find.

Is the probe still working correctly. I would check that 1st.