yeah can def harvest like that. i just did my blue widow.
i don't own a ph pen or any of the such.
when i recycle my soil i mix in a bit of sweet lime which controls the ph.
i started off with fox farms ocean forest soil($25 a bag) supposedly ph'd to 6.5 which i supposedly perfect for a soil grow.
i either use rain water or melted snow for the most part but also use my well water about 20% of the time. i drink it tastes fine to me but cannot comment on ph.
i ran my blue widow on all organic super soil. but have run my pineapple express with a bi-weekly feed of dyna gro foliage pro.
but if your gonna just run bottles nutes like dyna gro, canna, jungle juice you have to adjust ph accordingly.
people who use bottle nutes on soil go water, nutes, water, nutes, water, nutes usually every other time water they feed.
so you can see where if the nutes/feed watering wasn't ph'd you could have problems.
but i choose simple route and have great success.