Yup... cories are primarily carnivorous, so if you are feeding them sinking algae pellets/tablets, that's not really good for them. A bit of algae is, but not as a staple. My cories do wonderfully well on "Wardley's Shrimp Pellets". These are sinking pellets and the cories are in amazing condition (breeding).
As also discussed any 'meaty' sinking food will be good, including frozen bloodworms.