Thanks for the post shotta12,
some of the roots are allready in the res. but the majoity are hanging in free air and getting moist due to the bubbles of the airstone.
May this be nitrogen toxicity? The leaves dont look too green but one plant curls its leaves a little bit. Im using 1/3 strengh of my nutes atm, with a ppm of 277.
These are my roots:
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