Please do not buy a sand sifter star as it is not what you need to help. In fact, it generally undermines your attempt to solve your sand bed problem. Do you have slime algae or something? Sand stars eat the microfauna in a sand bed, and then typically starve to death in nearly all but larger tanks (over 100g at least) in 9 to 12 months. The microfauna that they eat are the real champions in the tank - little crustaceans, worms, etc.
Can you tell us about your tank (water parameters, especially nitrate and specific gravity, lighting, circulation, tank inhabitants, substrate, live rock, etc?). How often do you do water changes - how much, and do you use tap water?
For sand critters, you are better off with sand sifter snails (ceriths, nassarius, conchs) and potentially other creatures....but not a sand sifter star.