You fellows are likely annoyed with hypothetical threads (like the hypothetical betta sorority that didn't happen because my dad changed his mind about the tank), but I like to plan ahead, so, here goes. My friend has a 20 gallon tank that she is thinking of selling within the next month or two. I told her that I would consider buying it from her. A 20 gallon isn't very big, but I was considering a hypothetical list of species. I would like a species tank, such as a school of cobra guppies, or swordtails, or tiger barbs. Another fish I considered is a smaller variety of goldfish. I think one ryukin or another species would be nice. I'll stay away from comets and read up on other varieties that need more water. My main concern is that goldfish are social and having one might not be a good idea. Has anyone ever kept a goldfish by itself?