This stuff is most prevalent on the bottom rocks. It's not in the sand bed so I don't think that it's cyno. Ive had it a couple of weeks. Par is roughly 200 at the top and not much at the bottom. The tank is 2 months post cycle from bottled bacteria, and I've dosed 1ml/g phyto everyday. My water is crystal clear. I can't seem to find others with algae so green on the rocks and not in the sand bed. What do you think? Nutrients are sky high from the rocks leaching. The timing of the green coincided with an algae scrubber but that's probably coincidence as it barely has anything in it. Current nutrients are .40 - 18.2 which are down from 2.0 - 70 post cycle. Im pretty sure that this algae is helping me normalize.