coco shouldn't be dry. it's not soil. It's also incredibly hard to overwater as long as there is drainage out the bottom.
you put them in coco, then took them back out? outside or re-transplanted -- hopefully not the latter. that would be a lot of stress for no gain.
among many possibilities, leaf curl can be caused by heat. the curl down and in could be an attempt to conserve moisture. various other nutrient related issues might cause such a thing.
here's the good: if you are new to coco, the fact your plants haven't turned a dark green and showed a salinity problem means you got some decent coco, most likely.
Those are big enough to feed, so start keeping that coco moist with a well-rounded diet, because you have to provide 100%. if you don't have a good hyrdoponic feed, you need one soon. it shouldn't require a bunch of products. 2 or 3 parts typically.
you don't let the top 1" dry. coco holds much less water than soil, that's why it's nearly impossible to overwater and tha tproblem is likely something else, like underwatering or heat or... start eliminating with the easy, non-invasive stuff first. give about 10-20% runoff. probably every other day, but go by weight of pot once you get in a good cycle. each plant will drink differently.
if it's dry on top, it's nearly bone-dry and the plant is likely about to wilt, if late in bloom for sure. early on you can get away with it i bet. it also messes with pH and nutrient concentrations... bad news.
smal plant, small appetite. first month from sprout you mix in a little pH here and there if you see any hint of darkness or toxicities showing.