Why does my heater look like this?

[LHAquatics]

Its still pretty new

 

[carsonsgjs]

Just looks like algae to me. It can grow on heaters just as it can grow on the tank glass.

 

[coralbandit]

See if it wipes off. Looks like algae IMO also but I would see.

 

[ticojpunk]

mine recently looked brownish inside and it turned out water got inside it.