I just nearly ruined a roomful last cycle, I was mixing up my Final Phase to start flushing, and I got a phone call and got distracted, came back in and started watering out of a 20 gal res. without checking the pH, (remembered near the end of watering, so I checked it - Holy Shit, it was around 8 or 8.1) when I entered my outdoor grow-room the next morning, the whole place had a slight haze of mildew everywhere and it just got worse and worse even after flushing with straight ph'ed water, Turned Beautiful healthy trees of Oasis and Blueberry into Complete SnickleFritz...LOL. It was a combination of High pH water, High Humidity and Cold damp night air being sucked in.
I will NEVER water again without checking the pH first