Yep, its aiptasia. Ways to control it are trying to inject it with one of the available aiptasia solutions, or even just mixing kalkwasser with water. There are also natural controls such as copperband butterflys(difficult fish that is hit or miss as far as aiptasia goes), raccoon butterflys(will eliminate aiptasia and then move on to eating corals), peppermint shrimp, and berghia nudibranchs.