Tank has been up about 3 months. Started with dry rock but added seeded media in the sump. These little things appeared a couple of days ago. They do not appear to be moving. There is another group down low attached to the over flow. I thought maybe limpets tho I have never had them so I'm not sure. They appear to have a shell but it is kind of soft and can be dented when pressed with a small object. I can not get them off of the rock using tweezers. I tried to scrape one off but they are so attached that they just tear apart when I try to remove theem. They are small, maybe 3-4mm. I'm not paranoid but want to make sure they are not bad for corals. This is the best image could get.
