I don't think you burned your plants, maybe you could lower your pH to 6.0/6.2. I think you should give more bio grow and eventually stop bio roots. In my opinion, it is very difficult to burn a plant with Biobizz. When you see your stems with that violet color instead of green, it is a sign of deficiency. About your leaves, I think they are okay; sometimes it could happen to have some spots. Or if you have a fan that's too strong pointed at the plants, that could be it. Good luck :)