Exclamation Point Rasbora - Boraras urophthalmoides
The underrated cousin of the Chili/Mosquito Rasbora!
This is the perfect fish for your nano tanks. They do not grow bigger than 1 inch or so.
They love slow moving water and a tank that is heavily planted. Males will become more vividly colored, especially when competing for females.
They color up in a larger school (8+ fish) and do well in a nicely aquascaped tank with plenty of plants.