Here's something else to think about. You mention that they "perked up" when you let them dry out a little. This often leads to the idea that they're too soggy, overwatered, drowning... Often leading to reduced watering. roots dry out and get some air, plant perks up. Hooray. Or sometimes not. Usually, these "perk ups" are rather temporary, as allowing your coco to get too dry brings it's own set of issues.
Instead, it's more commonly effective to water more frequently to resolve these types of problems in coco. Coco is not soil, and can't be treated as such. It's a hydroponic medium through and through, and you're plants get everything they need, including oxygen, delivered by your nutrient solution. If a plant isn't developed enough for the pot, or isn't uptaking as quickly as it should, the moisture in your medium becomes depleted of oxygen. You can wait for the medium to dry enough for some fresh air to get to the roots, at which point you get that "perk up". You've also now got dried, mostly insoluble nutes left in your coco. The nutrient profile of the next feeding is shot to hell by this, as is the PH in the root zone. Now the plants getting watered again, but again it's screaming "WTF!?".
Or, you can just feed on a schedule (rather arbitrary), never allowing even the top to dry out, and avoid the above. My pump runs every 2 hours.
Someone else on this site said it best about coco:
"If you think it's dry, water it. If you think it's wet, water it".