The vet recommended Zolcal-D for our Cham, we feed it to him once every day. ReptiCalcium should be fine, but you should be dusting at least one of his feeders with a calcium supplement every day as long as it has no extras in it.
For veileds I dust the insects with a phosphorous-free calcium powder at almost every feeding and twice a month with a phosphorous-free calcium/D3 powder and twice a month with a vitamin powder.
I feed/gutload crickets, superworms, etc with a wide assortment of greens and veggies and a bit of fruit.....dandelion greens, kale, endive, escarole, carrots, sweet potato, sweet red pepper, squash, zucchini, berries, apples, pears, melon, etc.
Appropriate temperatures play a part to because they need the heat to digest the food properly.