Most starfish need mature tanks with lots of live rock. In a new tank they will starve. In a small tank, they will starve. Easiest starfish would be serpents and brittles, but they aren't going to take care of any algae or film. Sand sifting stars eat all of the beneficial creatures in your sandbed, and then they starve.
Once your tank is cycled and has a few months to mature and become stable, you shouldn't see the brown film anymore (diatoms). Until then, good old elbow grease should help keep your glass clean.