Vitamins: How often is too often?

Hi all,
Just bought some reptile vitamins (Herptivite with beta carotene by Rep-Cal) yesterday after learning it might be a good idea to give my snakes and other herps some vitamins on occasion.
I have no idea on how much to give my snakes, and how often, though....... I have two snakes eating small-large mouse hoppers and 2 bp's eating small-large adult mice and a snake eating jumbo adult mice or small-medium adult rats... idk how much vitamins they need...

There is absolutely no reason to give a BP any supplements. All they need are rodents fed quality foods. If you are concerned with the nutrition of the rodents you are feeding then I would suggest looking into breeding your own feeder rodents, and feed them high quality foods.