Excess light will not cause these symptoms... the red stems are usually from a deficiency of magnesium or calcium which will also show up as bruising on the leaves and, if not taken care of, will cause those leaves to die and fall off. The real question here is WHY you're getting this deficiency... and it's not because you haven't been providing them to your grow because you have... sufficient amounts of both nutrients are contained in your grow nutes. Usually, the problem is with the pH but yours is spot on for coco - so I'm left with thinking you're giving them too much nitrogen and that has caused a lockout. Since you're growing in coco, I would recommend giving them nothing but pH'd water for a week and then resume your nutes - but cut down on the nitrogen-heavy ones a little bit going forward. You're going to want to cut back on them again a little bit when they go into flower.
Good luck - looks like you've got your hands full with lovely ladies!