Rockwool is known for two things...retaining water and needing to be pretreated to the correct ph before use. It really should NOT dry out two to three times a day. Do you have them sitting on something warm maybe ?

Did you pretreat the rockwool by soaking it overnight? That will really help prevent ph issues with it. Otherwise you can get the irregular and uneven growth you're getting here......I can't really tell which problem it is......