Weird Brown Rocks, Dino? Cyano? Need help identifying!

thisnthat · Oct 5, 2021

I started my tank back in June 2021, and I got a coral light 2-3 months ago and ever since then I’ve been getting a brown film on my sand bed and rocks. I currently have 2 clown fish and a fire fish. For my cleanup crew I have 7 hermit crabs, 4 blue leg, 3 Scarlet reef. I thought ever since I’ve gotten this ugly brown film it was the the dreaded ugly phase every aquarist wants to skip, but I’m starting to think it’s more. I tested my nitrate and it came to 0, which was concerning until I realized I have Xenia and leptastrea, (my only corals) which both prefer dirtier water and absorb nitrate. I also have cheato in my refugium and those all play part in my nitrate reading. I have a couple pictures of the brown algae like substance and some parts are more stringy than others. There’s also some on the glass that go with the flow of the water, and even though I wiped it down they came back. I also rotated my sand bed while doing a water change and it seemed to move back to the top again. If anyone could identify what type of algae this is, and how to slow the growth and kill off most of it, please let me know below. \/