[wildreef]

is this tank fairly new ?
thats "brown algea" on your tank walls / rocks , typical to get on a new tank , if you have no live stock , turn your lights off' perform water changes, etc.

if you have live stock, fish, coral etc.
then you might try a few turbo snails,a lawn mower blenny , a midas belnny, tang ?
etc.
if its not much ' dont get upset' its natural' you most likely dont have hardly any coraline algea on the tank glass,
be paitent and in time it will subside, and keeping up with scraping, the algea off the glass for now will help.

also if the tank is aged and this seems to have bloomed on you all of a sudden , you might look into how old your bulbs are and consider changing them .
all bulbs will change "spectrum" over time and some spectrums encourage that sort of algea growth as well.