Haha thanks for asking dude, I've been killing it with my diabetes though, I won't let it hurt me down the road so I do everything I can now!
You'll see a major difference in growth from soil to hydro growing. Its beautiful. Even with autos, you'll get a good yield since you're running in hydro. For pH you'll actually want to be between 5.6-6.0 for hydro.The sweet spot is 5.8! And yea, better water with less TDS will usually buffer pH better. You never know what solids are dissolved in the water, so we don't know what could be reacting with the pH up/down to make it more or less effective.
I'll be watching tho, I'd love to see you grow some monster autos!