What are these !

[saltlife97]

Found these guys on my carbon on the bottom of my reefmat not sure if they’re pests or good but I also found one on a coral the other day that seem stressed please let me know what to do and what they are

 

[mtfish]

Pineapple sponges. No problem.

 

[saltlife97]

Pineapple sponges. No problem.

Will they kill corals

 

[Reefer_kano]

Will they kill corals

I just found them on my tank also, i was told they are harmless

 

[Mikedawg]

Harmless and will probably disappear on their own; enjoy them while you can