This page should tell you enough to discourage you heavily from using the stuff..coupled with a few friends of mine who have lost leos to long term impaction.. and short term impaction because they didn't listen to me. There's a forum somewhere where someone called "eyespy" happens to have posted veterinary surgery reports on sand impactions in older geckos that were proven to have built up over years of being on sand of any kind.. but this page is just an expirement someone did.. and its what convinced me never to use the stuff...
www.pythons.org/calcium.html

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Lucien
1.1 Columbian Redtail Boa (BCI)(Sutekh and Isis)
5.11.Leopard geckos (1.2 Blizzards (Caine, Phoenix, and Mirage), 0.2 Tangerine Albinos (Tequila Sunrise ...Tiki for short, and Casper), 1.0 Tremper Albino (Mycah), 0.3 Poss. Het. Albino (Annika, Lace, and Aris), 1.1 dbl. het blizzard x tang albino (Malice, Malfeas), 1.0 Full Stripe Chocolate Tremper Albino (Discord), 0.1 pastel (Raven) and 1.2 Normals)
0.1 Savannah Monitor (Kiros) (R.I.P. November 18, 2005)
13 rats (plus pups)
2 Dogs (Loki and Storm)
2 cats (Ashe and Hercules)