It depends on how light your hair naturally and what tone of orange it is when you're done. Getting a strong 40 toner can be good if your hair is naturally black or almost black. If it's more medium brown to blonde or almost blonde then closer to 10 or 20 might be better. It also depends on how brittle your hair is too. After all of that bleaching 40 might not be best if it's about to fall apart.