For store bought fish foods, it's best to read the ingredient list. The first 3-4 ingredients should be whole protein and plant matter. Typically, if grains or fillers are in the first 3, it's junk food.
That said, I've been feeding my severum and oscar Hikari Bio Gold + pellets for most of their lives as their main staple food. They've always been vibrant, active and healthy and the ingredients list is not impressive reading on Hikari products at all IMO.