Check out the flushing sticky at the top of Problems. Don't flush at pH 9. Use pH 8, flushing with a correct pH Up product, until your runoff reads ~6.4. I don't think your tap water is actually 9; the water utility would not allow that- check your meter calibration.
What is the hardness of your water out of the tap?
How large are the pots your plants are in, and how tall are the plants, and how many main branches/tops per plant?