soil PH in veg is 6.2-6.5 in flower 6.5-6.8, again a PH of "around" 7 is "around" to high. Some plants can deal with it others cant, one pot may have got more of the buffers than another pot. Treat each one as an individual, and deal with its needs.
You measure the pH inputs. Easy as. Don't bother with measuring runoff pH.
Don't ask me how to use a pH meter that is +/- 0.25. I'd bin it.
Apera have an Amazon store. Get storage fluid and calibration fluid in the same order.
If you are giving nutes also consider the PC60 instead of the PH60.
Don't bother with the Bluetooth model.