Is this harmful?

[fugzz]

Hey, i just bought an additional 3kilo's of liverock for my 20galleon tank and growing on one particular piece is what looks to be a silver silky algae coating... Im not sure what it is, but it looks like a layer of silver silky algae or something? If any1 can identify this for me that would be good, and what i should do about it? and if it is harmful?

 

[phoenixofthepyre]

it would be easier if you gave a picture... from the picture i have in my mind its just some sort of sponge maybe? or maybe something on the rock had died and is now just "melting" away.