Diatoms? Brown crust over rocks

[SomeHappyFish]

 

[Mr. Mojo Rising]

I'm not sure what I'm supposed to see here, can you post other pictures? How old is the tank? Can you share parameters?

 

[BristleWormHater]

Doesn't look like duatoms to me.
Maybe cyano or an encrusting sponge?
Need white light pics though.

 

[SomeHappyFish]

I'm not sure what I'm supposed to see here, can you post other pictures? How old is the tank? Can you share parameters?

The dark brown stuff on the rock?

 

[SomeHappyFish]

Doesn't look like duatoms to me.
Maybe cyano or an encrusting sponge?
Need white light pics though.

It doesn't brush off and feels slimy.
No bubbles.

 

[SomeHappyFish]

It can be scrapped but not brushed, I just tried.

bump