I could not find any researches from credible sources that indicate it is better for the frog to separately dust Calc. & Vitamins. So, scientifically it may not yet be proven. But, like Jess from IvoryReptiles said, I find it MUCH easier to control each supplement by dusting them separately, plus, it doesn't hurt the frog to dust separately. I can only see it to be potentially beneficial to the digestion of those supplement instead of harmful. Summing it up, it's completely fine to follow the herptivite instructions but it's highly recommended to dust separately like everyone is saying on here.