Benzelsanswered grow question 3 years ago U need more calcium in coco than soil as coco sucks up calcium and wants to hold onto it. I can see your plants already need trace elements from the leaf color. so get a good Cal Mag nute and a trace element nute as low iron can also be an issue. Start using trace element mix or cal mag and trace mix asap.
Dont water too often in coco either- every 3-5 days for pots and plants this size be fine for now.
And feed often with weak nutes not rarely with stronger nute mixes. No more than 50% strength til pre flower. its easy to add more nutes if the last feeding wasnt enough with another feeding but its very hard to remove too much nutes from the coco. And most pple suggest U go plain water, water, feed, water, water, feed ect with coco, and so do I, but if you feed and it doesnt look right u can go water and then feed again and then go water again and that should fix prob. At this stage they dont need lots of nutes all at once, more of a drip feed often ok.