Let me atest to how much damage these stars do I have a pretty big tank with about 5" of sand. I had LOADS of great worms, etc in the sand, but I wanted to resolve the 'algae on the surface of the sand' issue. I put in three sand sifter stars, and not two months later the sand was white, uncomfortably bright white. I noticed no worms (looking through where the sand met the glass) no anything. Anyway, nitrates and phosphates were fluctuating and it was very difficult to regulate them (and I've got a skimmer big enough for a 500 gallon tank!).
Long story short, after since I pulled them out, its been about 6 months, and the sand bed is just now recovering. An alternative that I used is a SINGLE bar (sand sifting) goby. He keeps the surface looking white and the tank looks great. Most people make the mistake of putting more than one in a tank, and they will both starve and not know what happened. With a 150g tank, go to LFS and get a small-medium bar goby, and he'll do the job!
