Well keeping anything a tank that is not suitable isnt good lol.
But maybe something for the starfish person to check out lol. Would be cool to find out as it would save ALOT of stars lives.
My petstore had prob fifty of these things for sale orange, blue, burgandy and formia and I wanted one so bad but I knew it was a no no for my tank. I have the rockwork just not old enough nor want to put something in my tank for it to die. But it would be awesome to find out some kinda food source they eat then you could soak them in vitamins to get all the extra stuff to keep them going.