What is this grey stuff?

[katonge]

I’ve looked at other threads on ’grey stuff’ but this looks different. I’m wanting to move this rock to the new 220.6 to help with the cycle thing but don’t want to introduce problems already.

 

[Tired]

I would guess a sponge. Poke it with something other than your hand, see what it feels like.

 

[katonge]

It has a web-like texture

 

[Sharkbait19]

Definitely a sponge

 

[katonge]

So leave it & move to the new tank or scrub it off?

 

[Sharkbait19]

So leave it & move to the new tank or scrub it off?

Looks like a harmless type. You could leave.

 

[Goaway]

If you plan to put corals on that rock, scrub it off

 

[Tired]

Scrubbing it off with a toothbrush might be good, some encrusting sponges can grow over corals. It'll probably just come right back, but you'll have inconvenienced it and hindered its ability to be potentially annoying.