Water PH starts at 6.5 but drifts to 8 over night. How should I set ph?

Hey guys, I'm about to pop a sprouted seed into some living soil for my first go at Organics. I have both RO water and well water at my disposal. I worked out a ratio for how much RO to well water I need to get it to a PH around 6.5-ish but after sitting overnight, the PH drifted up to 8!

My question is should I adjust my RO to well water ratio to accommodate the drift, so maybe add more RO to lower the PH or should I just be concerned with the initial PH since I'll be watering immediately after mixing the two?

Thanks for any advice!

If you are growing organic/living soil, there really isn't a need to ph your water. The soil will adjust it for you.

But the water probably has some dissolved co2 in it which is lowering the ph until it outgasses.

I have the same issue with my water. I don't adjust the ph. I don't have issues with my soil (I've tested the ph of the soil and its fine).

Don't ph the water. Ph is set by what is in the mix. Adjusting the water dues but change the actual ph in the root zone nor does checking runoff ph tell you anything useful.

Irrigation water pH affects chemical solubility of solutions, but has little effect on medium pH. Instead, medium-pH is affected by water alkalinity, which is a measure of the basic ions, mainly bicarbonates and carbonates, dissolved in the water. Alkalinity can be thought of as the “liming content” of the water, and irrigating with a high alkalinity water (above 150 ppm CaCO3 of alkalinity) can cause medium-pH to increase over time.

I did a test with two water sources with ph drift, first was runoff from the roof, ppm was 24 ph was 6.8 I ph to 6.2 with egg shell calcium vinegar. Ph drifted to 6.8 after 48 hours. Second water used was well water at 280 ppm, ph down with egg calcium, 48 hours later ph was 7.4. It helps that the calcium I add in the egg shell vinegar is already acidic and adds calcium, whereas the well water holds its original ph extremely well and reacts over time to drift ph.

Two observations.
1) RO water can have a pH from 4 to 10 without it meaning much.

2) if you want to pH a res, run an air stone to strip out carbonic acid. Remeasure and adjust.