Rockwool needs to be pH'd to 6 before use. It is hydroponic, so subsequent waterings/.feedings also need to be adjusted. Once you transplant to soil, that changes. At that point, give pH 6.7 feedings. It also contains NO nutes whatsoever, and you'll want to start feeding at a 1/4 strength (or less to begin with) grow fert. They look scorched from heat and need to be taken care of more often at that age, especially in bright sunlight.