Here's how we used to mix our discus fish food. We'd put all the ingredients of a small batch together. We'd then shovel, rake and hoe the ingredients together until it look mixed. Then we'd grind up the discus food mixture again.
The problem with mixing the fish food this way was that it was never really a consistent mixture. Plus, it was hard physical work and very time consuming. We finally solved this problem by purchasing a commercial mixer. Our commercial mixer works so well, that we only have to grind our food once now. The food is thoroughly and evenly mixed.