Originally Posted by ConorM
I am planning on starting a 20gal and was looking into bigger fish, but a tank full of tetras would be cool. It will be a mixed tank (20 fish, 10 species should work, right?). I want you guys to list some different kinds that aren't big or expensive. I would like interesting shapes and colors. NO NEONS PLEASE! If your suggested fish is hardy enough for a cycle, tell me. I appreciate any help.
Tetra are characins, and all are shoaling fish. This means they live in large groups. In the aquarium, they must be kept in a group, most suggested no less than 6 per species. The fish has an inherent need for a group, so any fewer can mean stress, weakened health, increased aggression--and generally very unhappy fish. So 10 species with 2 fish per species is not going to work.
A 20g is not a lot of space, so depending upon the species, one or maybe two at most will fill it. Plants will help both the fish and the water quality.
Most of the commonly-seen tetra are roughly the same mature size, 1.5-2 or 2.5 inches. But there are smaller species, like the Ember Tetra, and some pencilfish. With these fish, you can have more in a 20g.
Check the species in our fish profiles, under the second tab from the left in the blue bar across the top. There is a section named "characins" and the tetra and pencilfish are there. Hatchetfish is another group.