This is a discussion on What is this? within the Saltwater Aquariums forums, part of the Saltwater Fish and Coral Reef Tanks category; -->
What is this? It might look different because the light was of and didn't want to mess-up the cycle....
Looks like nuisance hair algae. Mexican turbo snails will help eat through it. Look for the source like high trates, trites or phosphates and eliminate the source.
