those look like little feather dusters to me, but they may be a hydroid species. Definetely NOT aiptasia.
Now back to bj5z25, since it was originally his post. If you go with peppermint shrimp, you want to make sure they are Lysmata Wurdemanni.
Another effective method is Berghia nudibranchs, they feed ONLY on aiptasia but die when all the aiptasia is gone.