If you go to a beauty supply store, you can buy liquid (not creme) hair developer. It is hydrogen peroxide in different strengths. 30 volume is 9% and 40 volume is 12%. Those would probably be best to use as normal hydrogen peroxide from stores isn't strong enough at 3%. Use gloves, put the peroxide all over the cage, let it sit for a while, then spray it down. You can/hear see the peroxide bubble as it's working.