Here is the reasoning behind us recommending dusting with a phos. free calcium powder at most feedings, phos. free calcium with D3 twice a month and a vitamin powder with a beta carotene (prOformed) source of vitamin A twice a month, gutloading/feeding insects properly, providing appropriate temperatures and proper UVB lighting for the umpteenth time.
Since many of the feeder insects we use have a poor ratio of calcium to phos. we dust with a phos. free calcium powder to help make up for it.
To ensure that the chameleon gets some D3 from supplements without overdosing it, we dust twice a month with a phos. free calcium/D3 powder. D3 from supplements can build up in the system and lead to health issues. D3 produced from exposure to the UVB light will not as long as the chameleon has the opportunity to move in and out of it at will.
We recommend a vitamin powder with a beta carotene source of vitamin A because prEformed vitamin A can build up in the system and lead to health issues. This leaves the owner to decide if/when the chameleon needs a little prEformed vitamin A.
Crickets, locusts, roaches, superworms can be gutloaded with/fed a wide assortment of greens such as dandelions, collards, endive, escarole, kale, etc. and veggies such as carrots, squash, sweet red pepper, sweet potato, etc. Feeding the insects well will help give the chameleon the nutrients it needs.
Providing appropriate temperatures will aid in digestion and thus nutrient absorption.
All of this together should help you have a healthy chameleon.
You can do things other ways but if its not within the right parameters you will suddenly find yourself with a lot of health issues in your chameleon....just because it appears to be doing well when you first start doing it a different way doesn't mean it won't lead to issues eventually where as following the most often recommended ways, used by many of us for long periods of time and with lots of chameleons seems to produce healthy long-lived chameleons. The choice is yours.