Pest or harmless?

[jythong]

This has been with me for more than one year, as a hitchhiker. Not causing problems and growing slowly, rather hardy thing. However I am just afraid it may be some kind of colonial hydroid but it does not seem like it as it tends to be encrusting, even encrusting onto the wall. What is it?

The specimen is question is the large brown structure in the centre of the image.

[CFOh]

try goggle porites to match. Shld be safe. Cheers...

[cedricang]

Bro i used to have this in my frag tank...and it spreads fast. I decided to remove it as it is rather unslightly and not sure if it will cause a wide spread and a threat to my corals.

If possible try to remove it.

[jythong]

Thank you guys for your advice. I think I will probably remove soon.