Anyone Know What these Are
 

Got them growing all over just wondering what there called

hydroids, bad news.

?
 

:sad: Why

Cause they can sting the @#%& out of your other corals if they come into contact!

Take a look here, from what I hear they are a PITA to get get of.

Hydroids are bad if you have any type of coral. They multiply and spread very quickly and will sting and kill coral. If you have a fish only system they are not harmful.
They are very hardy and can be just about impossible to get rid of. I have even heard of people taking a blow torch to their rock trying to get rid of then (not recommended).

They can spread indiscriminately through the tank and they burrow into the rock so simply scraping them off doesn't get rid of them (they just grow new heads). Corals tend to do poorly if these are with them in the tank.

Get out a hammer and chisel, its the only thing I've had any success with. I am running an epoxy experiment right now (epoxied over a whole batch) but I can see a couple sticking out at the edges of the epoxy so not a grand success :neutral:

how close
 

Does anyone know exactly how close they have to be to sting?

Did they arrive with your live rock?