leaf taco

I have 8 clones in solo cups with coco and 2 of the clones have this taco going on. I’m using 1 60 watt autocob about 3 feet above the plants. Using RO water and cropsalt veg nutrients ph 5.8 ... could this maybe be from the coco drying out too much between waterings?

Please any help would be greatly appreciated desperately would like to keep this baby alive! This is my first time growing in such an interesting location and I am not an experienced indoor grower. Below I have 3 photos 2 of the baby grapefruit 15days from seed under 12/12 and another random...