Buy a turkey baster and spot feed him. I wouldn't add anymore Purlple up till you buy a test kit and test for Calcium,and Alkalinity not a good practice adding suplements without knowing the levels. I maybe wrong about this but I would say the the Green algae is eating all the food and thats why the coaline is dying off. Use pre-cured rock, most fish stores have it. It might start a mini cycle but you should be okay. didn't know Wal-Mart sold RODI water, going to have to check that out till I get mine installed. Buy more snails, I have way more snails then crabs, I feel that they are what helps keep my tanks algae free. adn I agree with what amcarrig says about the starfish.