I bought some sinking pellets for my Cories, after reading in an ad that they might get malnutrition only feeding off of flakes that sink to the bottom. So I dropped 2 or 3 pellets in, and my 3 Cories didn't show any interest; my Angelfish and Betta went and ate it after it sat on the gravel for a few minutes. Now I'm rather skeptical; was this ad accurate or not? Just for further purchases, I am wondering if these catfish need this or not. Thanks.