cardinals school pretty tightly in a larger tank. In a tank like 36" long, they are everywhere. But with space like a 6 foot tank, they gather up and form tight school.
If I could "like" your comment, I wouldTheres also the option to go for two similar kinds of fish that wont school together despite looking like they would.
The Harlequin Rasbora (Trigonostigma heteromorpha) and Espe's Rasbora (Trigonostigma espei). When their schools intersect, its neat to see fish racism at its finest