A couple things to start...
Can you get pics in better light? HPS is very difficult to work with for diagnoses.. natural daylight would be better
What exactly IS that soil mix, and have you yet checked its pH, or flushed them since the burn?
6.3 is actually on the low side for a soil grow.
Let's start with figuring out your soil pH.
Since you are only giving nutes at 1/3 strength, we're going to fix that problem and get you back up to a higher conc of fertilizer, but only after you find out what your runoff is.