Looks like they're "praying" for magnesium in my opinion. Are you using the Advanced Nutrients Grow-Micro-Bloom? If so, what ratio are you using? The magnesium is in the Grow, so if you aren't using any Grow during flowering you may want to add some (say a 1:2:3 ratio of Grow:Micro:Bloom) and/or supplement with epsom salts or cal-mag.

You can also try foliar feeding with the epsom salts (1 tsp/gallon) to see if your plants pick up if you don't want to fart around by adding it to your res. Make sure you don't spray any water around the lights when they're on though (cold water/hot glass/not good).