theexoticvet:

I have never seen a reptile that had hypercalcemia (too much calcium) from oral supplements. The danger of hypocalcemia (too little calcium) is far greater and I always recommend dusting of food. It is very difficult to provide too much calcium with oral supplements. You can absolutely overdose and cause problems with injectable calcium. 

Dusting every feeding is not necessary though and every other feeding or so is more reasonable. Also make sure you aren’t making little cricket ghosts-they just need a very thin layer of powder.

I know lots of keepers that supply a small dish of calcium powder and in theory it should be fine, I have never had luck with it and it just sits there unused. Just make sure you are keeping it clean and replacing it often.

Make sure your calcium powder is just calcium with no added vitamin D. You can overdose vitamin D as well as other vitamins. Maybe once a week a vitamin powder can be added to food. Repashy Calcium Plus is a good calcium supplement with added vitamins. I like that it has pre-formed vitamin A in it as some reptile species have trouble converting beta-carotene into usable vitamin A.

Gutloading can be done with commercial cricket foods or you can provide fresh veggies and some low fat dog kibble.

Finally, I highly recommend a low output UV bulb even for leopard geckos. Reptiles need UV light to “unlock” the dietary calcium and make use of it. No amount of supplementation can overcome a lack of UV. I know leopard geckos are touted as not needing UV, but recent studies indicate even nocturnal reptiles absorb and use UV, they are just better at using very low levels.

TL;DR: Use a calcium supplement every other feeding. You can use a multivitamin supplement once a week or so.