i use the same mixture as dark angel, however, i hope no one ever has to use 4 L's worth of mixture in a year.
assuming its only for a few snakes, use a 1/4 of the nix bottle, to 1 L of water. That keeps for one year. then use the rest when you need it.
i prefer using a lighter solution and spraying every day for the first week. then twice a week for a few following weeks.
Grant van Gameren