Don't give up on your plants...
Your plants are short on Mg...you need to either foliar spray Epsom salt or add it directly to their feed water.
You need to hold tight on going to bigger pots...coco grown plants can and will grow better in smaller pots.
You need to keep your coco moist by eventually feeding them at least once a day...if not more. If you let the coco dry out, the salts in the coco concentrate and you get burn.
Be sure you buffer any additional coco you use in the future to remove salts and to help satisfy coco's appetite for Mg and Ca.
So, make up your nutrients as you have always done (pH @ 5.8...add some Epsom salt into the feed (maintain your pH)...water the plants to run off...and leave them alone. Tomorrow, if the coco looks / feels moist on top, leave them alone. The following day if the coco looks / feels moist on top, leave them alone. As soon as the coco looks / feels dry on top...feed them again (this doesn't mean dry the pots out...it literally means just the top of the coco. The coco below the surface will / should / needs to be always moist). Before long you'll have to feed them everyday and you'll be a happier grower...but until they get better, you'll have to baby them just a bit. Be patient and have some faith. Good luck.