Quinoderm is Benzoyl Peroxide, I used it when I used to get spots when I was younger. Seriously I cannot stress this enough, use 2.5% and stay away from 5 and 10% - research shows that 2.5% does exactly the same as its higher concentrations without leaving peeling, red, blotchy skin.
If you do use 5%, use it VERY sparingly at night before you go to bed. If you don't use it sparingly, you'll know about the effects in the morning when you wash it off - excessive peeling, bright red face, stinging etc. The thing is though, after those symptons subside, and your outer layer of skin peels off (takes about 5 days) your skin will be almost clear. But if you work, attend school/college/university, then I would strongly discourage you from using above 5% because with the effects it leaves on your face, you will be too embarrased to leave your front door!
2.5% is fine, but after applying it, apply moisturiser.