Is it safe to use debrox every night?

No: If you are doing this to prevent or control wax build up in the external ear canals, debrox will eventually produce an irritation and even inflammation of the skin of the ear canal. Wax is important to have and it is protective against bacteria and fungus. The ears should be examined periodically and only if you have a lot of wax, let an ENT doc examine and clean it.