What size tank is this? Corys like to be kept in bunches, at least 5, I'd say is good.
Assassins will also breed, but it takes a good long while. I started off with 7 assassins and now have about 40, most of them wee babes.
When you no longer have pest snails for them to consume, be sure to toss algae wafers into the tank. They love them.
75: blood parrots, featherfin cat, emperor tetras, turquoise rainbowfish, BN plecos, japanese trapdoor; 46: WCMM, gold inca snails, ghost, bamboo & amano shrimp, kuhli loaches, rummynose & ember tetras, endlers, platies, flame gourami, guppies; 16: pygmy, peppered, loxozonus corys, otos, assassins, RCS ... ~ Research PRIOR to purchase.... ~