Encrusting what???

[Deleted member 143833]

I've seen something new in my tank and I'm trying to ID with limited success and while I'd love to supply pictures they would be of little help so I'll try and describe what it is I have...

On many rocks there is a moderately firm, reddish-brown growth over the face of the rock. It is not move in the current, does not blow off and does not come off with a brush and has no real structure to speak of.

It doesn't peel of the rock but I can scrape it and and when I do that the rock under it is very white (almost like what ever this is has consumed part of the rock surface). It feels spongy but not thick; < 1/8. It doesn't appear to grow any thicker, doesn't change day over night but is growing across the rock. It does not collect bubbles and does not appear to be toxic to critters like snails and crabs.

It doesn't appear to be bothering any corals and I don't see anyone trying to eat it.

I can scrape it off and I would best describe it as sponge. If I was to take a guess I would say I have some type of encrusting sponge but I've never heard of anything like that...

Is there such a thing?

If you have any ideas or links to what you think it might be I would be much appreciative.

I did search through Sprung's Algae book and it isn't in there.

I'm stumped...

 

[Thanks Don]

It's hard to say without a pic but it sounds like a sponge to me. There are many things that can grow out of our rocks. Is it growing fast?

 

[Deleted member 143833]

It's hard to say without a pic but it sounds like a sponge to me. There are many things that can grow out of our rocks. Is it growing fast?

No, it doesn't appear to grow very quickly.

 

[jimsplace]

Following along, I think I have the same thing your talking about, I have always assumed it was some sort of algae. My alk spiked very high once and it all disappeared but has since came back. Seems like it does not like bright light or completly shaded, most of mine grows on the rock edges lower in the tank.

 

[mrpopo]

Def sounds like a sponge. i have seen encrusting kinds like you describe in many different colors.

 

[Deleted member 143833]

That is what I am thinking as well. The area I scraped 2 weeks ago still has not covered over so whatever it is the growth rate is very slow (as I understand sponge is). I think if this was algae it would have quickly overgrown the scraped clean section of rock.

Thanks