"Livebearers" will do well with a variety of frozen foods. These are the most nutritious, because they contain no additives. It's just the frozen animal and water. Flaked foods have "man made" chemicals added to extend the shelf life of the product. Look at the contents. There will be a lot of fancy names and such. If I don't know the contents, I pass on the product. Feed the foods with a short, understandable list of ingredients and your fish will be healthy.
"Fear not, my young apprentice. Just change the tank water."