IMO (and experience) it's cyanobacteria being bubbled up by the maturing DSB. I set up a DSB and it is going on a couple of months now. It's in my basement pond, and I periodically stir up just the surface. The only things in the sand bed are pods and worms, I don't have anything to eat any algae in there or to stir up the surface. The cyano is catching the bubbles as they come up and that is what is causing what you are seeing. If I remember, you just set your tank up recently, and your DSB is fairly new as well. From what I have read, this will go away once the DSB is matured and properly processing the nutrients in your system. However, I would get rid of the cyano (I peel it off and since it's filled with bubbles, it floats up to the top, very easy!) and look into the increase in flow and also, how old are your bulbs? My cyano is partially due to the fact that the bulbs are pretty old that I am using (just ordered some new ones in fact). I am getting away with it because there are no corals (a couple hitchhickers on some LR is all) in my system, only macroalgaes, some LR, and sea horses (and around 1000 mysis frye that I just introduced, although they're all over the system now thanks to the wind we had today knocking the power out and draining most of the refugium into the main pond). I find that cyano is caused by the excess nutrients that your DSB is not ready to process yet (phosphates especially, don't know if the DSB can process those), low flow, and insufficient lighting (often due to older bulbs).
