Yellow leaves with brown spots

I have recently switched the bulbs and switched the light cycle to 12-12. The plants have started flowering, but the leaves are turning yellow on one plant with brown spots scattered on the leaves. Pictures are below, there are 3 plants, the tallest one is budding the most, but has the yellow leaves with brown spots. Any help on how to solve this problem would be appreciated

Yellow leaves, brown spots
http://www.flickr.com/photos/60446895@N05/5514869205/

Same plant w. yellow leaves, brown spots
http://www.flickr.com/photos/60446895@N05/5515463848/

Purple from nutes coming up through stems
http://www.flickr.com/photos/60446895@N05/5514870523/

Close up of buds on plant w. yellow leaves
http://www.flickr.com/photos/60446895@N05/5515465854/

Other two plants, much greener
http://www.flickr.com/photos/60446895@N05/5514873985/

Close up of bud on one of the other plants
http://www.flickr.com/photos/60446895@N05/5515480248/

what kind of lighting did you switch too? or did you just change the spectrum?are you still adding nutes?it could be mites

Its currently under a HPS light, and I am no longer adding nutes. I dont think there are mites, I have checked several times

check pH ........

should the pH of a flowering plant be about 6?

Any where from 6.2 to 7.0 is ok for dirt. DWC is around 5.6 to 6.2

i tested the ph of the soil and it said it is near 6.5 - 7.5... any further help?

This is the same problem i have i thought slight nute burn but ive eased off nutes recently and think it could be N def any one else think this?

anyone else think it is a N deficiency

No it is not an N issue yet but could be causing the symptoms. First your ph if it is 7.5 you got to get it down under 7 that could cause lock-up being that high. Brown spots and chlorosis (yellowing of the leaves) are both symptoms of nutrient deficiencies (calcium and iron). Many of the micro nutrients are unavailable at high pH (alkaline).

One thing I would suggest is to get a some Cal-mag and use it at 1/2 recommended every other watering it will supply micro nutrients (if the one you have doesn't have them) to make sure your plant has everything it needs to grow. When the plant doesn't have any deficiencies, it's stronger and can better withstand less-than-perfect conditions . Are you over watering?

i dont think its a nutrient deficiency, i thought i over-nuted if anything. what do you recommend for watering during the flower stage? perhaps i am overwatering

Go buy a cheap water meter at Wally world or use your fingers. If in pots just lift it up if light water. Your plants will start to droop when they need water.

what nutes are you using? did you switch them when you went to flower? what is the N-P-K of the nutes? where are you getting your water from?