First of all, I would like to know whether or not newts in a tank together harm or possibly kill each other. I had three newts in a large tank. Two were about the same size and one was slightly smaller. I had the smaller one first, and when I added the larger ones, I never noticed a real problem between them. Well, I came home one day, and the smaller one was missing. There's a very slight chance that he escaped, but I don't believe that is what happened. About a week later, I came home, and the less dominant of the two remaining newts was missing also, and I know there is no way that one could have gotten out. They were always happily fed, and I see no evidence of the other two newts left in the tank, so I am clueless as to what happened to them.
Now, I am worried about my one remaining newt. When there were multiple newts in the tank, he was always very active and fun to watch. Now, he sits in the cave all day and possibly all night. He is eating. I haven't seen it, but the food is disappearing, so I'm assuming he's eating, but I'm still worried about him. I don't know if it's possible, but he seems sad. That's the best way to describe it.
Should I take the chance and get him another friend? Is he just lonely or is it possibly something else?
Sorry this is long, I'm just worried and wanted to give all the details. Thank you!

