I have spent a bit a time (ha ha) staring at my tank this evening and notice some previously unseen critters. They remind me of little white sand fleas you see at the beach. They don't seem to get along with the brittle sea stars reaching out of the crevices in my rock. The biggest one is maybe a quarter of an inch. They are really fast zipping in and out of holes in the rock so there is no way to get a pic. I have NO idea what they could be. I really noticed them with the brittle when I was able to feed some seaweed to the brittle with a pair of tongs.