Leaf problem , (vertical, tubes with coco)

You see the system , PVC tubes filled with coco substrate, i have 2 600w (cooltube)
and they shine 9 hour each (18/6), temperature is 22 - 28 °C , moisture is ok.

Now half of the plants have yellow leafs like you see on the picture.
Is this lack of water , fertilizer or maybe oxygen in tubes? (tube diameter 11cm, volume 10L + 11L pots downside.

Thank for advice.

Over watering back off on the watering harf the ammount the timers on i have said it 1000 times these vericle systems are the worste on the market because the roots can become dry too quick if there is not enougth water been added the only way that this kind of sytem can be used to its full potential is to use a fogger that will send fog up the tube when the water is not been fed through the tube.Either that or the plants are not getting enougth water but i have seen a fogger used with this kind of set up but the fog went into the bottom of the tube and come out of the top this kept the roots just moist not so wet that they became sodden/.................tyke.......................

One pic looks like root rot and the other 1 looks like k deficiency. Which makes sense with this system. Ur plants may be fighting for root space already, and light seems to be lacking in areas also.
Im not a fan of vertical setups indoors.
That many plants in a thin pipe packed with coco? Not nearly enuf space 4 proper root growth on every plant. The plants on the top will get shorted on root space and water, the lower ones will get overwatered. Its so hard to balance these systems out, the manufacturer forgot about one key aspect, GRAVITY. Plus HID bulbs only penetrate light so far.