I just set up a 20 g tank with 3 platies, 1 dwarf gourami, and 2 female guppies. Also, I added a male guppy from a smaller tank that used to have just guppies. This almost 3 yo male guppy is the lone survivor and has been alone for about a year and a half. A few hours after moving him into the community tank, I found him just sitting on the bottom. I moved him back to the other tank and he acted fine. Is he just too old and set in his ways to tolerate others?