@IronGiant runoff is a coco thing it doesn't work with soil. You can buy a pH probe like the accurate 8, or do soil slurry tests. Slurry testing is what I do.
Equal parts soil (taken from about halfway between stem and edge of pot. An inch or so down) and the water source you use regularly. A couple tablespoons is plenty.
Let set about as long as it would take to run thru the pot, and then take its pH. (Careful, glass bulb and perlite don't mix well)
I usually take a reading 3 times a grow before planting, at flowering, and mid flower.
Many soils out there will drift low on pH as some things break down and our plants are feeding.
Just feeding @6.5 many times is not enough to stay in range.
This is where I start, if the soil pH is on spot, then we can look at deficiency/toxicity issues.
I use nectar for the gods nutes, my up is a liquid lime, so it sticks in the soil and helps correct low issues. Standard pH up and down is only meant to change the pH of your feed, and will have a difficult time bringing the soil pH up.