>>I have had these 2 leopard geckos for about 5 years now, but they have always been in seperate tanks because I thought one of them was a male. Well, I looked at "him" again today and I am pretty sure he is a female. Can I put them both in the same tank without problems? Will they fight and hurt each other or what?
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>>Thanks.
From your message, I'm getting the feeling that you know for sure that the other one is male. The short answer to your question is maybe. The long answer is that there are several factors involved.
First, if you put a male and a female together, be prepared for eggs, as they will more than likely breed at some point.
Second, both males and females can be somewhat territorial; if you're going to put two geckos together in an enclosure where one of them has lived for a long time, it's recommended to rearrange all the cage furniture so that they both think it's a new place. This will usually prevent territory-based bullying.
Third, is the tank big enough for two? Generally you want at least 10 gallons per gecko (a 20 gallon or larger tank for what you describe), and more is never bad. Basically you want there to be enough space that they can choose to avoid each other if that's their preference.
Fourth, make sure you have an adequate number of hides for the number of geckos; ideally you'd have a 2 warm and 2 cool hides so that they don't have to be right next to each other if they don't want to.
Fifth, make sure you supervise their first meeting and watch them pretty closely over the first few days to make sure that there isn't any aggression going on. If you notice anything that looks bad, or any injuries on either of them, you'll need to separate them.
There's probably more, but I think I covered the basics.
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0.1 Albino Leopard Gecko - Tigger
0.1 Crested Gecko - Pooh-Bear