There is no answer to this question!!!
1) Most importantly no one knows the exact nutrient requirements for even common species of chameleons (forget about the rare ones!)
2) The way that people dose powdered vitamins is not standardized. A "pinch" is a BS way to dose anything. How big is your pinch vs mine. How much sticks to the bugs? How much falls off? How long does it take the cham to eat the bugs? How much do the bugs ingest as they clean themselves vs how much falls off? Do you feed out of cup that is coated in old vitamin dust or do you feed in the cage? When you say that you dust every meal, do you feed daily, or every other day, or dump in a ton of crickets for the week? Do you dust all of your feeders or only a few? Do you spray your feeders with water to get the powder to stick? See where I am going with this...
3) Vitamins and minerals degrade over time and there is little quality control to start off with. Analysis have been done on numerous different brands of supplements and many do not have what they claim to have in them. More importantly they are inconsistent from batch to batch.
4) Everyone provides different conditions, temps, diets, lights, stress, ect. There is NO standard supplement schedule that will work for everyone.
There is a wide range of acceptable diet parameters that a healthy chameleon can make use of. Grossly too much and you can have toxicity and over supplementation diseases (Especially with fat soluble vitamins ADEK and certain minerals). Too little and you will get deficiency symptoms. But there is a wide range between those two that can work, depending on the individual animal, and the other husbandry conditions. All of the suggestions mentioned so far are close enough in the ball park to work for some people. I know successful breeders who never supplement and I know breeders who supplement daily.
So how is a person to choose when and what to supplement? I would suggest the following... Feed as varied a diet as you possibly can. Provide as much exposure to natural sun as you possibly can. If you can do both of these things, supplement very sparingly. If you cannot, supplement more heavily. Buy several different reputable brands of supplements and rotate them often. Err on the side of less supplement more frequently, as opposed to infrequent overdoses. Throw them away BEFORE they expire. Shake each can well before you use it. If they get cakey from humidity, throw them away. Keep them someplace dark, dry, and cool. Be cautious using too much of any powder containing preformed vit A.
Most importantly find experienced keepers, and experienced vets and ask them how they do things. Watch your animals carefully and let their behavior and health guide your decision making. Experiment with different schedules and see if you can tell a difference. Like I said... very confusing subject, and definitely no single correct answer.
