I don't know, as I'm not a hydro guy. Did you check your other thread for an answer to this same question? :wtf:

Looks a bit like overfertilizing or overwatering, but I'd wait till an experienced hydro guru comes along before making changes based on my guesswork. While you're waiting though...copy-n-paste the hydro troubleshooting form here, and fill it out as completely as possible.