[Van down by the river]

I'd have to say Christyf5 got it right=Echinaster echinophorus.

It has very little resemblance to any Fromia stars. I haven't seen the sprung picture but it is identical to a few found elsewhere.

Per Fossa/Nilsen:
They say it is a Caribean species reaching 7cm
"Feeds primarily on detritus and microscopic invertabrates,possibly also on algae.Will often not accept substitute foods."
Well you've obviously found the right substitute!

They go on to say it is mainly a shallow species ranging from Coral rubble/Reef/and Mangrove areas.
Fairly hardy once adapted to conditions.
As with many inverts they say it doesn't appear to be a problem with corals and inverts but it cannot be totally trusted.

This seems to coincide with the behaviour of yours quite well. References elsewhere suggests that this species or some of it's close relatives are attracted to light. Do you find yours is more active in the day?

Anyways you are lucky to have it in your tank.