More pH info. Check your runoff pH, and you have not said WHAT pH you are running.
When you say 'sort of' soaked, what do you mean?
Your problem looks like a classic example of improperly prepared hydroton. I don't know why the instructions are not on the bag- they SHOULD be. Gotta soak at pH 6 until it stabilizes, about 1-3 days, and then rinse before use. In your case, it's already installed, so you have to adjust your res pH back to 5.8 2x/day until stable.