It is probably simple but I can'tell what my problem is...

Just moved my healthy Pineapple Express plants into their flowering room. They are showing severe yellowing and spotting and comparing to these charts is not helping me at all. Here are some pics:

Temps: ~80 F
Humidity: 50%
CO2: 1400 ppm
Plants are 16 days into flowering, and Using Advanced Nutrients feeding program. was at 1200 ppm, but bumped up to 1600 ppm after observing yellowing. At a pH of 6.1

Thanks in advance.

Check for bugs under the leaves. Prob none but just check anyway they can leave marks like that as they suck leaves dry. Id water next feed with some epsom salt and and raise your PH its a bit acidic in my opinion. Try 6.5. Soil is a buffer do you know the soils ph? If you dont know it just be safe and water with a ph of 6.5.

They could be deficient in many different things but epsom salts are good a few times in flower anyway to prevent magnesium deficiencies. Also now in flower they should be getting plenty of P and K and not to much N but a little still to keep the leaves green at least upto the late weeks of flowering. Down to preference really... Check out micro nutrients and just make sure your plants are getting some of everything at a good PH the plant can use the nutrients nut dont over do the nutes just take it slow and watch for improvements. This problem is not to far gone you cant sort it.