[greenbean36191]

Agreed. One is most likely too many. They do such a good job of keeping the sand turned over because they're constantly searching for critters to eat. There are several species of star sold as sand sifters, and most of them don't eat anything you want eaten. Some will feed on detritus when other food is scarce, but it's not something they live off permanently. Others are so general in their carnivory that they have been used as a way to sample the diversity of the bottom. Others are extremely specific in their diets and only eat certain small snails or crustaceans that live in the sand.

In nearly all cases, a 120 is too small to produce enough food to keep even one alive long term. They eat the tiny critters that really make a sandbed work and then they can take up to 18 months to starve after they've exhausted their food, all the while showing no signs of ill-health.