What is this?

[deepblue]

Anyone know what this is? It’s on what used to be a zoa garden a long time ago. 

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[FutureInterest]

That is a sponge.  A very good thing as it means your tank is healthy.  Some can even be quite attractive.  I've got a jet black one growing in my tank that branches like acropora.

 

[deepblue]

Ok sweet. Thank you.

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