What is this?

[Loganstall]

@revhtree @Gumbies R Us

 

[AlyciaMarie]

Tiny sandalled anemone maybe?

 

[ISpeakForTheSeas]

Definitely anemones of some variety (and it does seem to bear some resemblance to the Sandalled Anemone, Actinothoe sphyrodeta, but that's a "coldwater" species only found in European waters) - you'd need clearer pics of the column/pedal disk (the stalk and foot), mouth, and tentacles to get a more specific ID.

If you want to try for a more specific ID, I'd suggest trying to remove one of the nems in a container of tank water for closer up pics (preferably against a black background).