Ya, the size of the tank and these fish does suggest that this could work. However, I do not want to chance it unless I hear others who have done so successfully, particularly adding a new toby to a system with an established one. I really love my blue dot and would not want anything to happen to him. Plus, two puffers going at it would get real ugly really fast resulting in a situation of substantial injury and/or death when considering their teeth designed to crack shells. Plus, if one of them manages to substantially injure or kill the other, I would be afraid that my other predators may feed on one of them and die from the toxicity of the injured/dead puffer which I bet is why your tank crashed.