mold/fungus issue in the rdwc

hey can someone help me out with this fungus/mold thing happening here in my rdwc. I have bleached and scrubbed the system and pipping (pump too inside and out) and yes a week later this appears again. could this be light issue ? i have only a clone in the system and it seems to be doing fine no mold has collected on the net pots yets just the walls and cluster around the pump out take as seen in the picture\

any advice would be nice

What products are you using in your nutrients? any beneficial bacteria that may have grown in the system?

Light able to get into your system somehow, or not enough water movement/oxygenation most likely

Was using GH flora series for the last grow in it but i more then cleaned it out. light cant penetrate the resivour bucket but my other system which is the same has no issues how ever there is no waterfall in the res as the other has one.. maybe thats it cheeers