This is a batch of live rock that keeps on giving! I got about 10lbs from the LFS of this almost a month ago to cycle my new tank. Almost immediately, I found that it was riddled with Aiptasia and a small amount of bubble algae. I took the rocks out of the tank and removed all the aiptasia and bubble algae and put them back in.
All of the rocks but this one appear to have stayed pest free since my cleaning. A few bits of aiptasia came back on this one that I'll be removing shortly. When I was looking at the aiptasia, I noticed something else growing on the rock.
When you look real closely, there are a dozen+ of these very fine strands coming out of the bigger pores of the live rock. On all sides of it too, not just one area. To the naked eye, it looks like alternating bands of black and white going up the strand. They seem to be growing longer every day. This live rock has some bigger chambers inside that connect to the surface through smaller pores.
The pieces near the aiptasia came out the clearest in the picture. If anyone can identify this, I'd greatly appreciate it!