ID Help

[Xtasia]

Looks alot like..




From Wet Web Media:
it is a fairly common nuisance hydroid, Myrionema... somewhat handsome looking to me, but is admittedly a problem... can be a plague. They will sting corals and clams and are invasive as you have noticed.

- I've seen alot of people with it. Not sure how to deal with it but all sources conclude it is invasive and stinging. Maybe take the rock out of the tank and use a tooth brush on it... rinse with RO thoroughly (maybe do a 'swish' with salt water in a bucket to do another rinse since they spread so easily and it appears your system is favourable to it)

g'luck.