I had similar and it got pretty bad. Was thinking it was dino but redish-brown on sand and webbing with bubbles. I haven't 100% got rid of it yet but I added more flow, fixed skimmer which was leaking from seal, spent the time to blow off the new growth on rock, added reactor with gfo/carbon and changed to 100micron socks replacing every few days. The initial ones I threw out instead of cleaned...horrible smell. I also added filter pads and sponges to keep as much as possible from going back to the DT. Lots of info on here talks about turning off lights. I believe flow and media are key and lighting is important to nems and macroalgae. I was caught in trap of turning off lights when cyno showed up and then all inhab. were unhappy with shortened day and lower intensities...so lighting reduction can be an issue if used as a bandaid over and over instead of fixing underlying conditions.