What's this Grey/blackish paste on rocks?

[Lui1521]

Hi! I'm new to this hobby and got this aquarium from a friend. I noticed that there's a greyish black paste like texture when removed. Not sure if this is something that would be ok to have in the reef.

Picture attached.

 

[Diesel]

Some sort of algae.
Is it easily removable?
Can't see it for sure but does it have little air bubbles hanging on it?

 

[Lui1521]

Easily removable like a paste. Attached is a farther view. Its the darkest parts of the rock that has an inconsistent white outline.

 

[Diesel]

When you remove it does it stay in one piece or large pieces or does it fall apart?

 

[Lui1521]

When you remove it does it stay in one piece or large pieces or does it fall apart?

It's sticky

 

[Diesel]

If so I think we talking sponge here.

 

[emap0225]

I would 2nd that[emoji115]I had a sponge pop up in my tank that looked similar from what I can tell from the pic.

 

[Diesel]

By increasing your light or lowering your nutrients the sponge if you don't like it will slowly decrease.
Besides it's a filter feeder and for that no harm, it just looks ugly if you ask me.

 

[Lui1521]

By increasing your light or lowering your nutrients the sponge if you don't like it will slowly decrease.
Besides it's a filter feeder and for that no harm, it just looks ugly if you ask me.

Thank you!!! I'm just worried that it might have been a algea outbreak right before my eyes!