what is this on my monti??

[Darth]

it seems to be on the damaged part of the coral you may have to zoom in on the pic, but you should be able to get an idea of what it looks like

[JD]

I have had pieces of coral get damaged, loose a small amount of flesh then have algae grow where the flesh used to be.
In those cases I just snipped off the damaged part and allowed new flesh to grow over before the algae takes over.
Is that what you are seeing?

[Darth]

def not algae not sure what it is here is a better shot at it hope it helps

[Rybren]

They look like they might be hydroids to me.  There are a couple of kinds - colonial and digi-something.

[JD]

I think your right, not algae. They do look like some sort of hydrozoan.
In any case, I think I would snip off the damaged area.
I am a firm believer of "if in doubt, get it out".

[OttawaReefer]

definitely hydroids. 

[Vincenzo.]

looks like coraline and hydroids