Runoff 6.0 is too low. You are looking for runoff 6.7.
In an emergency, cider vinegar or lemon juice work okay.

Following the instructions for a correct flush (stickied at the top of this section), you must:
-Aim for final runoff 6.7 in soil, 6.4 in soilless, and 6.0 in rockwool
-Feed immediately with a complete fertilizer mixed at 1/4-1/2 strength that contains micronutes to replace what you have washed out through flushing.