U need to feed live starfish. Some harlequin may just kill them within an hr. This is a problem cause ur tank may or may not have NH4 spike. In the wild, harlequin will not kill the starfish. It depends on ur luck.
When they are hungry, they will come out to search for food and this is the time u know they need to feed. Mine pair take 2 -3 week to finish one starfish.