Can anyone tell me what this is?

[xnaz]

I was working on my tank today and discovered some weird brown stuff in my third chamber? Can anyone help.

 

[Reefer5640]

It’s hard to see much detail in that pic but it kind of looks like sponge from what I can tell

 

[vetteguy53081]

May be simple slime and algae but as mentioned, white light will be of value to determine

 

[xnaz]

May be simple slime and algae but as mentioned, white light will be of value to determinIt’s hard to see much detail in that pic but it kind of looks like sponge from what I can tell

Is it harmful?