This is my first grow i have a tropicana banana grew from seed in a 15 litre pot (repotted about 10 days ago) filled with canna coco 60/40 under a 600w hps light it is getting fed around a litre of water every 2-3 days using canna a and b at 15ml and rhizotonic at around 7 ml per 10 litre the light schedule is 18/6 and i have an oscillating fan and a 12” outtake i do not know the temperature or humidity but it doesnt feel to hot in there the feeds ec is about 5.8-6.2 it is in the 3rd week of veg and the large fan leaves at the bottom have gone yellow and brown and are crumbling to touch and the ones higher up are yellow at the tips and/or curling over. It started early on I have attached pictures from differant stages if it helps they are with the lights on and i cant take any more at the minute
From your first photo it looks like the plant is getting too much light, it looks like the leaves are curling down the middle. 600w is a lot depending on how far you have it away from the plants. Just from the photos I can’t really tell what’s going on, if you can bring them in another light that would be great.
It could be a couple of things off the top of my head, one being pH level. When you say ec do you mean pH? If so try staying below 6. If not it might mean that the plants is getting too much Nutes and it’s getting nute burn. Try diluting the solution a bit. Also are you using DI/RO water? That could make a difference. Tap water, and even filtered water, could have an Ec of 350 which is like a quarter to a half of the recommended EC. All EC is the ratio of nutes to water.