Found a small aiptasia on one of the frag plugs earlier. It was removed and scrubbed off via toothbrush with extreme prejudice. No idea how it got there, but I'll be keeping a closer eye on the tank for a while. Fortunately, since there are no wrasses in the tank, berghia nudibranchs are a potential option if the infestation gets too large, but hopefully that little one is a one off, and no more of them pop up...