Red-brown algae or sponge growing on rock

[billysprout]

hi friends, any idea what this could be? i thought it was a sponge but it seems to be filamentous in lower light.

siphoned a sample into a petri dish and it fans out growth like a spider web. seems to be stopping at my corals but i want to check in with the experts to see if i should just siphon it out.

the zoa frag it came on died shortly after i added it to the tank, im not sure if it was caused by the growth or just a normal casualty.

i have an urchin and snails and neither seem to be touching it. hope you can help!

 

[littlebeard]

Looks like cyno to me. I would dose microbacter7 or similar and just watch it.

 

[billysprout]

Looks like cyno to me. I would dose microbacter7 or similar and just watch it.

thanks! i didn’t know cyano could be this color. i’ll point a powerhead at the spots if the bacter doesn’t help.