AquaRick said:+1 diatoms. They feed on the silicates in your system. They usually show up in new tanks.
Rutrag said:What you see is probably just the beginning. It will likely look like it will turn the entire tank to brown sludge and then will recede as quickly as it showed up. It's basically a form of algae.
Rutrag said:Generally speaking yes. I just scrape it from the front glass so it doesn't look too awful. They need silicate to survive, and that should be consumed in a week or two then they will begin to recede unless you do something to add more silicate like adding new sand.