For balls you don't need to worry about humidity as much as people do unless you come from a very dry area. You should be fine where you live. You don't even need to worry about his humidity levels or need to spray his tank at all and he will be fine.

BUT when he is going into shed you would need to bump up his humidity during this time to make sure he has a proper shed. When it happens you don't need to worry about the level either, just cover the majority of the top of the tank with a plastic bag and spray it down once a day until he sheds.

If you are worried about humidity you can also just give him a humid hide and he can regulate it how he wants. Just get a Tupperware with a lid big enough and cut a little hole for him to get in or out and put some damp moss inside. Again you don't need to worry about %'s with the hide. Just keep it most and if he want it humid he can go in, I he doesn't he can get out.