Droopy thin tips

Growing in coco using canna a and b at 2ml per litre
Blue dream from seed
Temps around 23C lights on (its getting to winter)
Feed ph'd at 5.8-6
Runnoff at 5.9
15l fabric pots

My third grow with coco the other two went well. This time I'm having nothing but issues with 3 blue dream and 1 cheese plant. 2 blue dream started fine and the other one and a cheese were really slow to get going. They still hqvnt caught up but as I wanted them done by Xmas I Flipped 4 weeks ago. Now the cheese is still small but looking healthy but the two largest blue dream are having issues. The tips are very thin and drooping down quite severely. I added Epsom salts earlier in the grow but I still have the odd brown patch on older leaves too but it's the tips concerning me. Iv never had this before. My last blue dream run was fine. This time roots are growing out of the bottom of my fabric pots so could I be root bound? Even in a fabric pot. Plants are around 2.5 feet so could be that. Or I suspect the coco is not draining and I'm having oxygen issues to the roots. Any help appreciated

Im not an expert with Coco, but here is my opinion. Not getting enough oxygen with coco is really hard to achieve. The plants actually look rather thirsty to me. How often do you water? How much do you water?

I water when the pot starts to feel light. I must admit a couple of times I have been busy and let it run an extra day which won't have done me any good. I water till runnof but the thing is they seem worse just after watering I can't work it out

if they dont get better 30mins after you watered then this is not the problem..