Does/ will is tank contain frogs? If so then you should definitely try to get rid of them immediately. Stone centipedes are voracious predators that will eat almost anything, (I've even seen them feeding on dead mice, mushrooms and pea sprouts) and they have a venomous bite like a wasp sting. Even though they usually stay out of sight they're not something you want a frog, especially a small one, trying to eat. The shells of adult woodlice are to tough for their forcipules to pierce but molting and young woodlice are fair game.
You probably won't be able to catch the centipedes by hand without tearing apart the tank. Maybe you could try tying half a mealworm or a meat scrap to a thread and leaving it somewhere you often see them. When they get ahold of something tasty they're reluctant to let go.
millipedes generally are harmless scavengers like woodlice, but some species secrete foul smelling and even poisonous toxins. There's one kind that doesn't smell and is accepted by insectivorous animals, which is fairly short, cylindrical in shape and moves quickly. However I doubt this is the species you have in there because stone centipedes enjoy eating them. Again, if you have frogs I would remove them to be safe. Especially if you'll be keeping tropical species that aren't familiar with the local invertebrates.