What is this thing?

[snotdoc]

I have these in my overflow and sump. Few in the tank. They still out and look like a small polyp extending. 3-4mm. What are they? Thanks!

 

[FutureInterest]

What we commonly call a pineapple sponge. They're beneficial imo.

 

[snotdoc]

Cool thanks!

 

[picoreefguy]

agreed its a pineapple sponge. they're harmless filter feeders. but they can be an indicator of over feeding if you see tons of them popping up everywhere.

 

[camellia]

They can also multiply quickly and become a magnet for scum.. in your overflow. I had this issue and just scraped 1/2 out with a bristle brush. Now I leave a small nano Krollia circulating in my overflow 24 seven and it is eliminated the problem.