What are these?

[ArialReef]

Just saw these today. Pretty sure it wasn't there yesterday. Any ideas?

 

[reef lover]

That's a neat one!! #reefsquad

 

[dbl]

@KJ...any ideas here?

 

[Tahoe61]

Hydroids I believe.

 

[KJ]

Look like Hydrozoa sp.

 

[ArialReef]

Are they bad? What should I do?

 

[KJ]

If you can remove this rock and soak in peroxide for a little bit and scrub good with clean brush. Then rinse good with RO/DI water and then put it back in the tank.

 

[ArialReef]

If you can remove this rock and soak in peroxide for a little bit and scrub good with clean brush. Then rinse good with RO/DI water and then put it back in the tank.

I can remove the rock but my high end mushrooms are stuck on it. Any alternatives other than peroxide?