I've been using the aquarium test kits (test tube - color indicator chart) for many years, and I do adjust my water first to 6.9 to 7.0, then add nutes. You can not add nutes, then accurately test with the color-indicator, unless nutes are clear. I've tried with Fox Farms, FloraNova, and (eek) Miracle Gro.

Adjusting my alkaline water (7.9 or so from the tap) to 7.0 gives me the ability not to worry too much about my nutes, additives or soil bringing the ph level too low. Keep in mind, tho...I flush at least once during veg, and at least once during flower to help correct any possible ph and nute build-up issues. Since starting to use the molasses, I flush a second time while in flower.
I'm on a fixed income, tho...and can not justify buying a new ph probe, when I have been able to live without one for many years.

Is this optimal...no. But I know my strains very well, and am very pleased with my results.

Also: Lack of grower stress makes the buds taste better, lol.