If I mix hair bleach and shampoo..?

Okay so I have purple hair, I used manic panic purple haze on it about a month ago. I'm planning on bleaching it tonight so I can dye it turquoise, but people have told me that if I mix the bleach with some shampoo it will strip my hair to a light blonde. Should I just use the bleach, or mix it with shampoo? Also, if I do mix the hair bleach with shampoo, how long would I keep it in to get it light blonde/white? Thanks in advance <3