Best to have you fill-out the troubleshooting form, as we'll be shooting in the dark with a diagnosis based on limited info. There's a link in my signature, scroll down to the Hydro Form. Copy-n-paste it here, and answer the questions.
-But-
Flowering plants need nutrients.
They need proper lighting. (proper lighting that can effectively extend to the lower regions)
And an overly humid enviornment (including misting) promotes mold. Moisture get's trapped between the tightly-packed budleafs.

Check the site FAQ's, and perhaps a few Grow Logs and the Hydro section, to get a better idea of what other's are doing for success.

Although yellowing fans is normal in late-stage flowering, 3.5 weeks in is a bit early for this in most strains. It's likely due to nutrients deficiency and/or lighting.