The small size of the tetra fish might mislead you into continuous thinking that keeping so many of them in a five-gallon tank as practicable. We would be looking at two main factors that make this a terrible decision to make.
Size: The principle that should be adopted when it comes to keeping small fishes like the tetra is the one inch per gallon rule, this means that one inch of the tetra fish is estimated to occupy one gallon in the tank but make sure you only apply this when the fishes are micro in size. The average length of most tetra fishes being about 1.5 inches, it is not a great idea to keep more than 3.
Shoaling fishes: Shoaling fishes are simply fishes that live in groups which are referred to as schools, for social and safety reasons. A tetra is an excellent example of fishes that live in ‘schools.’ Although they are a relatively peaceful species, they can quickly get agitated or scared when they are few.
A school of tetra fish is a set o 6 together. A five-gallon tank allows you to keep only 3 fishes which is not relatively equal to the school number, this technically means you need a 9-gallon container for one school of tetra.