Mine too! I tried several different brands, I stopped once I fed them Omega One, it was clear that's what they liked bestI feed my goldfish and Cichlids Omega One food and they seem to enjoy it quite a lot.
https://www.amazon.com/gp/product/B009POWM8K/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1