how do I get rid of this?

[derekbsu]

I think my rocks and sand are growing green and brown

algae

 

[snakeblitz33]

looks like part of a normal initial cycle process. the brown looks like what could be diatoms. the green is normal green slime. your rocks will turn many colors over the years.

 

[innerdragon103]

Just curious: did you start off with dry sand or live sand?