Another queation for Stinky or other experts

Is it the soils pH that needs to be around 6.5 to up take nutes or is it the solution of the nutes that needs to be 6.5 to take up the nutes?
I am growing in soil. The pH of my RO water is 7.4. When I run that through my soil (in 1 gal containers) my runoff reads 6.5 which is what I want. If I adjust the ro water to 6.5, the runoff reads 6.2 which is too low. So heres my question. When I add nutes to the RO water, I then adjust it to 7.4 so that my runoff is 6.5. Is this correct? Can my plants still uptake the nutes?

Note:I tried flushing couple weeks ago with pH 6.5 RO water (3 gallons per plant) to try to get the soil to reach 6.5 but it didn't help much. There must be something in the soil causing a low pH. Transplanting is not an option.

You're in peat based soil I bet.
Keep the soil pH at 6.5-6.8 and if that means watering with a slightly higher nute solution, so be it.
Now, when you take the water pH, are you doing it before or after you mix the nute solution? 'Pure' RO water with a high pH is indicative of an aging filter. The pH you are concerned with is that of the solution including all nutes and additives you are using.
I'd try to adjust your nute solution to no higher than 7.2, and still keep checking runoff.

I measure the pH before then again after I add the nutes. I get my water from an RO water dispenser (one of those machines in front of supermarkets) It says it gets serviced twice a month so I assume they change their filters. After i flushed a few weeks ago the runoff measured 7.0 but after the soil dried out and I ran some RO water thru it today, it read 6.2. So I don't think flushing helped much. They are very healthy though. My husband wants to put them into flowering because they're getting too big but I would feel more comfortable if i can get the pH straitened out first.

Good call to have confidence in your growing conditions before flowering.
I've seen people have problems with grocery store RO water. Let's just say I don't trust the store to service the machine properly. If it's used very heavily, the change needs to happen sooner than on a unit that gets only light use. If they aren't testing the pH and EC daily, they really have no business selling their so-called purified water, lol. Water that has been truly deionized and then allowed to air equilibrate will actually register a slightly acidic pH due to the presence of carbonic acid from atmospheric CO2.
Just occurred to me... is your tap water like really REALLY bad that you are running RO in a soil grow? That's not what people usually do. Tap water has minerals that the plants do need, and one of them is dissolved CaCO3 (limestone) that actually helps buffer the soil from becoming too acidic, and the plants REALLY need the calcium. If you are going to continue running the RO, you need to add calmag plus.
Think about switching to tap water, and on the next transplant, to a more stable soil mix.

My tap water's ppm is close to 500 right now. I've seen it as high as 600. I add calmag+ to my ro. I'm going to flush one more time to see if that helps. The soil takes about 5 days to dry out. If they get to big by the time I get their pH taken care of then i guess I can top them all.