hydroids, I guess...

salty joe · Apr 22, 2019

I have a green patch that mostly disappears at night, then comes back every day and is expanding.

Does that sound like hydroids?

Highgrade · Apr 22, 2019

Doesn't sound like Hydroids. Most Hydroids are clear/white in color and will still be there with the lights off. Sounds more like algae of some sort. Pics would help.

salty joe · Apr 22, 2019

Sorry, not much of a pic... It's about 3 x 4 inches. It's a short, dense, tight layer of 'fuzz' that is just long enough to move in the current. Kinda looks like felt. A nice deep green.
It practically disappears at night and every day it returns to all its glory. Snails, urchin or hermit crabs don't seem interested.

Highgrade · Apr 22, 2019

salty joe said:
Sorry, not much of a pic... It's about 3 x 4 inches. It's a short, dense, tight layer of 'fuzz' that is just long enough to move in the current. Kinda looks like felt. A nice deep green.
It practically disappears at night and every day it returns to all its glory. Snails, urchin or hermit crabs don't seem interested.

Not too sure on this one. Most likely an algae of some sort. How long has it been coming and going?

salty joe · Apr 22, 2019

It showed maybe a few weeks or a month ago. I just took a good look and it has bubbles. Dinos maybe?

Highgrade · Apr 22, 2019

salty joe said:
It showed maybe a few weeks or a month ago. I just took a good look and it has bubbles. Dinos maybe?

It's a possibility. Usually Dinos are snotty/stringy. You mentioned it is more like felt or velvet? Sounds like I could be Green Cyano. Cyano does have air bubbles also. Can you blow it off or suck it off the rock?