Hey!
The calcium that the feeders are dusted in, is to balance the calcium to phosphorous ratio to a usable level.(2:1 if I am not mistaken)
Most feeders are the opposite, 1:2. If there is too much phosphorous, the calcium will be unusable. So most or all of the feeders should be dusted.
For a panther chameleon, this schedule is generally recommended.
Calcium without phosphorous or D3: Everyday.
Calcium without phosphorous with D3: Twice a month.(every other week, on just one feeder)
A multivitamin supplement: Twice a month.(every other week, opposite the D3 week, on just one feeder)
Repashy Calcium Plus is an all in one, and can be used alternatively to the schedule above. It is good stuff.
Its important that the roles the different vitamins play in the body is understood, so you can properly ascertain how to supplement your chameleon.
This is some great reading:
https://www.chameleonforums.com/blogs/olimpia/573-chameleon-physiology-supplements.html
https://www.chameleonforums.com/blogs/bridgofaith/320-most-used-links.html
When dusting feeders, you want to coat them EXTREMELY lightly.
I have found that swirling them in a mason jar, with a small sprinkle of supplement to be the easiest way to accomplish this.