I wouldn't reccommend putting them on sand. Thats great that they are eating out of dishes but that won't stop them from eating the sand. Wait til they are older before switching to sand, if you do decide to do it.
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1.1 Bredli Carpet Python
2.4 Columbian Boa morphs
2.1 CA Boas
2.2 Argentine Boas
1.0 Savannah Monitor
0.0.1 Nile Monitor
1.0 Leopard Gecko
1.0 Hermanni Tortoise