this is what you call cyano, check your p04 in your tank. check your rodi water where ever its coming from should be 0 or close to zero. or maybe you need more flow in that area. i recommend to do wc and suck out as much as possible dont stir it up because it will get distributed everywhere else in the tank
also forgot what type of bulbs are you running? mh t5? of they are old they it will help grow algae like this