Red Eye Tetra Query?

They are aggressive. Most fish stores have their fish marked as docile or mildly aggressive or aggressive. Those tetras are probably best suited with fish twice their size or with cichlids. there isn't anything you can do about it unless you want to get another tank. They should do fine in groups of the same type but you can't mix docile with anything remotely aggressive. You should always ask the temperament, because that pretty 5 or 10 dollar fish could end up being fish food as soon as you turn your back.