algae ID please

[Madkix]

I've got two zoa frags in close proximity to each other that have been closed for about 5 days and I'm trying to figure out why. I'm wondering if this stuff is the culprit, though the other frag is pretty clean....

 

[Drummingbaker2010]

I've got two zoa frags in close proximity to each other that have been closed for about 5 days and I'm trying to figure out why. I'm wondering if this stuff is the culprit, though the other frag is pretty clean....

I'm not really sure what that might be, but in the future, I might recommend low to moderate water flow via a power head to prevent it from happening again. I'm sorry I can't be more help than that just yet.