What's wrong with my plants?

I can't decide between nitrogen or magnesium or what. They are almost 4 weeks into flower. The strain is purple cream with a 9 week flower time. My temps have usually been between 65-82 lately with humidity between 25%-45%. I'm running 3 600W HPS air-cooled lights in a 5x9 box with 29 plants. This is my first actual grow ever and first grow in a while(had a 6 month hiatus).

If I had to guess I would vote for a pH issue. Also it looks a bit overnuted so you can back off them a bit as well. Whats your pH going in and runoff?

it could be a N deficiency, as most flower nutes contain little to no Nitrogen. It could also be a slight K deficiency, as the plant uses loads of this for flowering. what pH is your water? Are you using tap, RO, distilled? they look really good for a first time grow!

CallMeJack said:

it could be a N deficiency, as most flower nutes contain little to no Nitrogen. It could also be a slight K deficiency, as the plant uses loads of this for flowering. what pH is your water? Are you using tap, RO, distilled? they look really good for a first time grow!

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Ph is about 6.5. I'm using tap water that I run through this "Boogie Blue" filter I got at a hydro shop; it's supposed to filter out the chlorine and chloramine and other toxins.