Would A Bigger Shoal Make Cardinals Less Shy?

Are you asking if more cardinals would make them swim as a group, or if more of them would make them swim in all parts of the tank?

It is possible that more of them would make the cardinals swim all over. I have noticed that my related green neon tetras (Paracheirodon simulans) tend to keep to the back of the tank - except when they can't see me and then they swim all over. If I sit in the armchair and keep very still, they behave differently from when I stand in front of the tank. Do you watch your fish from close to the tank or from a distance? In other words, are your cardinals doing the same as my green neons?  It could just be in the nature of Paracheirodons to hide if they see something large moving near them, in which case upping the numbers won't help. But you could try an extra two or three and see what happens. No more than that or you'll have too many fish.



But adding more won't make them swim as a group, if that's what you meant. Schooling (ie swimming as a tight group) is defensive behaviour and most shoaling fish only school when threatened. Some shoaling fish do school more than others, but cardinals are not among them.

It might well be Paracheirodons. Even when I'm watching from the chair, my green neons may come to the front but they are still in the bottom half of the tank. If you are happy with your fish layers I would leave them be.