Curling leaves can be lots of things Chris. Overwatering, too much Nitrogen, too high a temp, etc.
Just keep doing what you're doing, they're lookin fine.

A couple of things, Once the roots start showing out of the bottom of the nets, you only want to fill so that the water is licking the bottom, then let the roots follow the feed down. You dont want the rockwool constantly soaking.
The other thing, the small seedling at the front of the back right bucket, is that powdery mildew or just a trick of the light? Looks to have some white patches on it.