I keep a 5gal bucket of water in the flowering room. I have a fishtank bubble stone in the bucket to aerate it. This does several things, increases the humidity in the tent, puts a lot of extra oxygen that the plants love in the water, allows the chlorine to evaporate off, and oxygenated water does not allow the growth of anything nasty in the bucket. This is water right out of the tap and is right near 7.0 ph.

When I water, I take a pitcher out of this bucket of the amount of water that I know my plants need. Every other time (in flower) I add nutes to this pitcher, and every time, I adjust the PH of this water to 6.4ph using ph up or down. I also have gotten away from buying the ph stuff, I use pickling lime from the grocery store for ph up, and battery acid cut 15:1 with distilled water as my ph down... both, a whole lot cheaper than the products you just purchased.

I do not test my run off, because that number doesn't mean anything to me... it is no longer affecting the plant. I simply adjust the ingoing water to the proper range, 6.3-6.8.

You however are not using soil now, you are using pure perlite, and this is something that I have never tried. I did try hydroponics for a while, but I was way out of my comfort zone trying to put everything in the water that the plants could need, and not having the stable base and natural buffer for my mistakes that soil provides.
For my gardens, I know that the microbials in soil have a lot to do with the health of my roots, and I am not at all sure if that natural process can even work in 100% perlite. Someone with more knowledge than I will have to advise you on how to grow in that artificial medium, but I assume that it is going to be similar to how you would work an ebb and flow or similar system, and if so, your ph will need to be adjusted to those ranges. I am curious to see what you come up with, and will be following your next grow very carefully.