yes, i have witnessed both the eating, and the depletion of the amount of powder left in the dish.

i personally use rep-cal in the green jar, but any brand of pure calcium without D3, assuming your gecko is eating CGD, will work.
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4.1 snakes, 4.3.2 crested geckos, 0.1 gargoyle gecko, 0.0.2 red-eyed tree frogs, 2.0 devon rex cats, 1.0 betta, 0.1 sun conure, 1.0 lovebird