Spaghetti worm or hydroid, or ..

[sd_tom]

There may be multiple things going on, but I do know peroxide dip (200ml to 1L) doesn't do much for the geometric ones in the middle. It does seem to knock back the stringy things on left.. to regrow.

 

[shakacuz]

left seems like hydroids, right seems like sympodium coral or clove polyp

 

[sd_tom]

Interesting thought.. hmm