keep in mind that tetras are schooling fish and do best in groups of 6 or more. in that small of a tank, another platy or two, or a male guppy (more colorful than females.... and its hard to find just females, but if you can, go for it), or a molly or two. an adf might be nice, or a snail of some sort. maybe a couple of panda cories since they stay nice and small.....................