Depends on your tap water ph. When using chlorinated tapwater, just sitting it out for a day or so allows the chlorine in it to evaporate. (if you can't smell it, it's fine) I used to fill-up a 5 gallon bucket with the lid off, and let it set for a day, was fine this way for a couple of years. I'd much rather use the tap, if at all possible. Consistent, cheap, no trips to the store lugging water around...

You can't accurately test runoff ph with dipping strips or aquarium tests. They're color-coded, and the slight discoloration of the runoff skews results. Keeping ingoing water at between 6.6 and 7.1 or so. With the addition of nutes, should be fine. A ph meter and calibration solution are wise investments, eventually.

Read the schedule closely, as it looks like you've missed the mark already, lol. Grow Big is a veg nute, not for flowering.

Would vent as much as possible, too. They need the CO2 from the fresh air.