Sponge?

[JLH-l3ioCub3]

I have two different colors (purple and white) of this stuff that looks to be sponge-like because of its porous appearance and it's growing in various places in my tank. The most prominent is the white colored and it's starting to concern me a little because it seems to love growing on my corals. It's not ONLY on my corals, it's just as much on the rock. The corals don't seem to be bothered by it and open and close normally as they always have. This sponge-like stuff has managed to give way to the polyps to open. Attached is a pic of it on my Green star polyp, and pipe organ corals. Notice on the pipe organ that it's elongated. Some other areas form like this as well, but nonetheless it's still porous like the rest.
Could this be sponge? If not, could it harm the corals?
BTW corals are closed because I turned the lights on at night to get a pic. Otherwise you can't see it because when opened they completely hide it.

 

[BelleMorte]

No clue what it is but it does look very interesting to say the least..I am going to be watching to see what people come up with as it looks really neat

 

[Bige]

Purple looks like gsp (closed). The white thing is a sponge.

 

[JLH-l3ioCub3]

Purple looks like gsp (closed). The white thing is a sponge.

Yes that is my GSP coral.
I'm glad you see the white stuff as sponge... That's what I was thinking! It's porous with just 1 or 2 holes in it that I think it filters water with like sponges do, but I don't know much about sponges....
My LFS had some big sponges for sale last week and this stuff looks just like it; just smaller.
I just can't understand how it's spread onto my corals.

Anyone else have this stuff in their tanks?
Could it be something else?
Should I be worried about my corals?

 

[Bige]

Sponges grow. It was probably somewhere on the rock and just grew up. I have some in my sump that appeared and are now 3 or 4 inches long. I have white and black ones.

 

[JLH-l3ioCub3]

Cool! Good to know. Thanks!