I had 2 full grown male capra in a 18''x18''x18'' exo-terra galss terrraium along with another female. And none of those dragons where enven near as happy as they are now. Overall they are more active, eat better, pretty much are healty in all aspects. Now, the female lived in there for a while on her own, and did just as good as now... so three might be too much... I think.
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Ryan