Please see the answer I gave to Gnugs87 (nitrogen deficiency.??....purple kush), a few questions below this question on this same page.
It is an almost identical situation/question.
It will explain what I think is going on with your plant too.
Hope this helps, Organoman.
From the top we cant see your leaves that well. but I think I can see them pointing down. Let the soil dry out a bit, then half your watering or double the days in between watering to let them recover.