Bubble algae? ...

[jgvergo]

...but why? I have not changed anything or any process in my tank for months!

 

[Dr. Reef Verified Sponsor]

It could have come on anything. Rocks, corals, inverts etc. Might have been sitting dormant due to lack of nutrients or light etc and now it's starting to grow.
Best remedy, take that rock out of the system. Brush it well and burn it with lighter in that dedicated spot rinse and place back.

 

[jgvergo]

I have not added anything for 6-7 months and my feeding has been lighter that usual. My lighting schedule has not changed.

I'll try taking a lighter to it!