They are fine solo. They aren't really social, to males will not like each other. the dominant one will chase the other off. It's nothing serious though they are so slow it's like watching 2 really out of shape people try to chase one another. They won't go very fast and they give up after of couple seconds. I have 2 males, wanted a pair one died and was replaced with a male albino as a gift thinking they were the same exact fish. If I did it again I wouldn't have 2 but it's not a issue because of what I said before.