I fed my last harlequin constantly. He always had a sand sifter or linkia star in the tank. He started with the arms, eating 1 per day. When he got full or ate 2 arms I would rotate the star into my fuge to regenerate. I had 3-4 starfish at all times in different stages of healing.
If I forgot or he dragged the star where I couldn't get it, he finished the whole thing in a week leaving only dorsal skin or parts of the body.
A few times I forgot to feed him for a month. He cleaned out some pest starfish I had in my tank. As soon as I placed a fat starfish in he would sense it, come dancing (literally) out of the rocks, flip it over and beat it like it committed a crime.