This seems to me to be more of a soil type grow and ppm concerns are geared more toward hydro with a reclaiming feeding system, although I can see some pertinenance being you are just using rockwool. Now in my opinion, not that the nutrients you are using are bad, which they are not, but I would get some fertilizers that are formulated more toward hand feeding and if your are going to hand feed I would recommend using a good organic soil with bone meal and earthworm castings in stead of the rockwool.

It does look like some of the tips are burning a little bit to me but it also looks like your plant wants more root space. How many plants are under that 1000w?