White fluffy ball with hole in it... what is it?

[red_roadster]

I have a number of white or cream colored balls that look kind of fluffy and have a single opening in the top. They are attatched to the rocks.
Any ideas?
Thanx,
Red

 

[007]

Try doing a search for Q-Tip sponge or pineapple sponges . . . .

 

[kinkfish]

I used to have a ton of these in my tank now I dont have any any reasons why?

 

[007]

Same here . . . one day they just vanished

 

[fender]

They tend to come and go with calcium levels. High levels seems to be what these guys need. How high? Don't know. They have popped up and disappeared in my tank a few times.