Yeah, I know these are not technically plants, but I have chosen to include them here because I am lazy. They appear commonly in ecospheres as a brown coating on the glass, but don’t worry, they should eventually go away on their own!
If you want to get rid of them quicker it’s best to use an LED lamp. Snails can also be used, but I have not had much success with that. Diatoms will probably linger in small amounts providing food for many of the mollusc species.