No longer a newbie.
Did you rinse your sand first? Looks like residual powder from your sand stuck to algae and biofilm
I've used dragon stone a lot in my earlier scapes. It is inert and doesn't shed anything like that. If it isn't rinsed well the residue is orangey brown and looks like clay dust, not white so it definitely isn't from the hardscape. I've never seen anything white like that, even fungus from driftwood is more milky clear than it is white. Perhaps powder fertilizer? Did you treat the tank with any kind of medication? What about inside your canister/filter? Do you have any media in there that could have eroded down a bit or didn't get rinsed well? I know ceramic rings and the like usually come in the bag with residual powder. Can't think of anything else white like thatSomething in your hardscape could be leaching minerals into the water column. I'm not that familiar with Dragon Stone, but it looks like limestone, which could be the problem. What's the substrate?