Is the white stuff like mold? I heard a white mold happpens in Hydroponic systems due to so much humidity, I also heard it's damaging to plants...

I don't know though...

But you might want to clean your rocks and somehow lower the humidity?
HumoredSanity Reviewed by HumoredSanity on . Possible Plant Problems Thus far I have recieved great and right on advise. I have followed to the T. I see signs of stress or something with the older leaves. This plant is so dense, that the top Fan leafs are blocking light. Also I am geting a buildup of a white substance on my rockwool. If I am missing anything, please let me know. Day 27 from Seed to What you see Setup is as follows: T5 Lighting System 10 Gal Eb and Flow PH 5.0-6 PPM Unknown 24 x 7 lighting Also thinking of pre-flowering and Rating: 5