10 Neons in a 5.5 gallon?? I guess. Why bother? The 5.5g cost almost twice as much as a 10gNeon tetras with good filtration maybe lol
You'd put 5 Neons in a 2.5 gallon? I'd do a Betta and maybe a Cory in a 5.5g, and a Betta alone in a 2.5g, but I GUESS you could do a Cory or Ottocinctus