What is your pH? From my limited experience, it looks like nute burn. But nutrient burn can closely resemble many things. First off, an imbalanced pH can lead to similar die off.
I faced this very same problem a few weeks ago. With the tips of the leaves burning, that exibits magnesium/pH lockup/early nute burn.
However, that spotting you see...those circular spots away from the fading/burning at the tips...I believe to be a pH problem.
The mass fading, however, looks like either a mag/nitro deficiency. But both these "symptoms" can also be due to pH. What's your fert schedule/type?
Have you inspected your grow medium? Next time you water...immediately after the water has soaked into the medium...look for mites/larvae. You need to look long and close because it is very easy to miss. After you water, scrape the a bit of the topsoil away and look for little white/brown dots walking/crawling around.
If you see none...then I believe it to be pH and not magnesium/nitrogen deficiency because of the lack of upcurl on the leaftips.
Check out my post and respective links
http://forum.grasscity.com/sick-plan...h-problem.html
Hope this helps