Agree. There are some other issues to be aware of too.
First is temperature. This species, Mikrogeophagus ramirezi, including any of the artificial varieties (German Blue, Gold, etc) must have warmth. A temperature of 80F (27 C) is absolute minimum, and they would be better a degree or two above this. So that limits suitable tank mates, as many "tropical" fish cannot manage with such high temperatures on a permanent basis. Some suitable tankmates include cardinal tetra (Paracheirodon axelrodi), the false/green neon tetra [Paracheirodon simulans] but not the common neon tetra; the smaller hatchetfish in the genus Carnegiella, and some others I could think of given time. Cory catfish are out as they need cooler water, even the "warm" species are not advisable here. And cories would eat the eggs/fry at night anyway.
The rams occupy the lower half/third of the aquarium, which is also where the cardinals, etc like to live. The hatchetfish obviously are surface fish. Another possible is a group of one of the dwarf rasboras in the genus Boraras; these would remain in the upper half of the tank.
Colin gave the minimum tank size, and I agree a 30-inch (75 cm) length would be much better.
A pair must select their own mate. Any male/female will not necessarily bond, and that means a dead female before long (usually). If there are a number of rams in the store tank, it is possible to observe likely bonded/bonding pairs. If you buy a group of fish, say 8-10, and let them pair, then you have to do something with the "leftover" fish and that is not easy unless you have several tanks.
