Actually those plants DO look perfectly fine, if a touch yellow down low.
Putting rockwool in dirt, I personally prefer to leave most of the cube sticking up so it can dry out completely and prevent rot at the base of the stem.
If you already gave them a grow fert, you should be fine especially since it was at a low dosage. Just keep on with the bloom ferts and make sure the yellow doesn't get much worse until about a week or 2 before the harvest date. After that, all bets are off and yellowing is not anything to fret over.