Is this black sponge?

[Kunala6]

This is growing under my frag rack that is holding my acans. It kind of looks likes a sponge but thin. Anyone know what this could be.
Thank you

 

[ISpeakForTheSeas]

Yeah, looks like some kind of sponge to me - it's most likely harmless:

Yeah, that's definitely a sponge. Most sponges are completely harmless/beneficial, but some can be invasive and/or harmful to corals (thankfully, these are rare).

To tell if a sponge is chemically harmful: if a healthy, established coral starts closing up or looking to be in bad shape on the side closest to the sponge as the sponge grows closer to it, and nothing else has happened (lighting changes, parameter swings, pests, etc.) that could explain it, then the sponge is probably chemically harmful.

Chemically harmful sponges are very rare.

For invasive sponges: unless it shows signs of being chemically harmful or starts actively growing over and smothering a coral's flesh/polyps, it's harmless. These can grow over the skeletons of corals, around the base/stalks of corals, even up into the water column above corals (where they're over the coral but not growing on the flesh or polyps themselves), etc. without harming the coral at all - as long as the coral flesh and polyps can get food, light, and flow, the sponge is harmless.

Invasive sponges are moderately rare.

Invasive and chemically harmful sponges are incredibly rare.

 

[Kunala6]

Yeah, looks like some kind of sponge to me - it's most likely harmless:

Thank you,
The Acans on top of the frag rack are healthy and shows no sign of stress. Hopefully it stays that way and the sponge is not harmful. Some of my bubble tip anemones hang out in the same area and they seem to be fine.
Will just have to keep an eye on it.