Best thing I could offer here is someone else's advice on how to correct lockouts. When you say you flushed the plant to 6.8, how did you achieve it? Did you use 6.8 water? What did that water come out of the container at?

Here's the link to Stinky's correcting nute lockouts.
http://boards.cannabis.com/plant-pro...hy-how-do.html