This is an interesting discussion. I don't know the answers, but look forward to hearing what others have to say. I probably water with a solution between 5.5-6. I've never measured the runoff though. I would suspect your mix is a bit higher than 6.7 though. The watering solution must be reacting with your medium and the resulting pH of that reaction is what you are measuring. I am no chemist though...

"The target pH of 6.0 to 6.5 for Florida citrus production
is based on a study of pH and Ca interactions conducted
on a ridge soil (Candler fine sand). A clear advantage of
pH 6.0 over pH 5.0 was evident, and pH 7.0 was no better
than pH 6.0 at all Ca levels. Therefore, if a soil test does
not show excessive copper accumulation, a soil pH of 6.0
is sufficient for citrus production. Soil pH should be raised
to 6.5 when soil tests show a build-up of copper because
this element becomes toxic at low soil pH.
Soil pH can be increased by applying either calcitic or
dolomitic lime. In addition to affecting soil pH, calcite is
an effective source of Ca, whereas dolomite supplies both
Ca and Mg. Therefore, although either calcite or dolomite
could be effectively used for citrus production, the choice
of dolomite would be more appropriate for soils that also
require Mg."

From: https://edis.ifas.ufl.edu/pdffiles/SS/SS47800.pdf

So I would say you don't want to keep the pH lower than 6, based on scientific evidence, with a range of 6-6.5 being ideal. This is highly dependent on the chemistry of the soil as Laura mentioned.

Before you get concerned about your pH, what did you use to measure the pH and what is the specified accuracy of the method you used? If it was an instrument, was it calibrated and what was used as the calibration standard?

Also from https://edis.ifas.ufl.edu/pdffiles/SS/SS47800.pdf

Here, the thicker the bar the better the uptake of nutrients at that pH. Notice the ideal range of 6.0-7.0 for nutrient uptake.

Thanks for the sources Stefan, some very good information in there. Now I just need to find a way to test my soil(locally)

Vlad , used a pH meter I purchased at my local hydro shop. Accuracy to .05pH. I used the instructions and 7 and 4 buffers to calibrate. I also called my local water commission to ask what my pH at tap should be and my meter matched.

I understand there are probably better meters out there with better accuracy but I don't need to be that specific.

Bmelz, it's the pH of the fertilizer solution that is most critical than the pH of your soil mix which changes constantly...That is why many drop the pH of their fertilizer solution every time they water with vinegar or some other sort of product when it comes to containers...

What's in the ground, the soil when pH is critical more so...

Interesting. But it's still important to have a balanced pH in your soil, that's why the 5-1-1 ads the lime.

Also, I've ready many post in here discussing the vinegar( which I would use) but I have pH down from the hydro store, so might as well use it, if necessary.

Great info Stefan! Thanks for finding that out. I wonder if some of the nutrient issues I had with a few of my trees were that I did not add enough lime (dolomitic). The first time I made the 5-1-1, I did not add the lime. I went back about a week later and scratched it into the soil. I probably did not add enough though.

Bmelz, yes that's true, but I mean once the soil mix is all ready made with the right pH..Sorry I didn't make that clear)