Close up would be best, but looks like some cyano. Getting really good flow helps with that as well as some snails that turn over the sand bed, like a tiger conch. It looks like a young tank, so cyano, diatoms and dinos will take advantage of that and grow over things. Getting more "nutrient consumers" in the tank can help get past this--examples: ornamentsl macroalgae like codium and pom pom gracilaria, some soft corals like toadstool, zoas/palys and (shudder) xenia. The latter, Xenia, does a great job growing and using up nutrients, but you may want to isolate it as best you can on an island so that it doesn't take over everything.Hey! My uncle recently dosed a bunch of stuff to his tank and that caused a HUGE algae bloom. As part of that he has been getting this weird film like algae on his sand that he keeps combing with a net but it keeps coming back. He asked if anyone knows what it is and if it would gradually go away with water changes and time.
