I have not read the whole thread....
But they DO NOT eat the bacteria in the sand.
They eat the creatures in a sand bed that keep a sand bed healthy and functional as part of your biological filter. This is destructive.
They DO NOT eat detritus and rarely will they take to spot feeding. In smaller tanks, most will starve in about a year, though their death is often mistaken for being eaten by something as they slowly disintegrate and lose large pieces of their body. Hermits and other scavengers will then be drawn to it.
I never, ever, never recommend sand sifter stars.
Sorry if it was covered already....I am at work and strapped for time