dont think that you can just let them kill the rest of the SPS and then they will starve. You have to manually remove all SPS from the system (and kill what you cant remove) for the AEFW to starve (which takes a couple months). If you leave even a bit of SPS, the population will just reduce and they will resurge when you reintroduce SPS. They can live in a kind of equilibrium with coral, keeping it from looking good or growing well but not killing it (survival mechanism).