Does anyone know what this brown stain is from?

[ZachDemitro]

I got this brown stain on the back of my tank and it seems to be on my rocks too. I recently dozed with copper is it possible that the copper stained my glass and rocks?

 

[carmodpg]

looks like algae to me

 

[exnisstech]

looks like algae to me

I agree

 

[CivicS14]

wait... back up. you dosed copper in your display tank?

also, maybe diatoms?

 

[ZachDemitro]

wait... back up. you dosed copper in your display tank?

also, maybe diatoms?

Yeah I don't have corals and don't plan on having any corals or invertebrates