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I couldn't find the right place to put this thread, so I hope this is in the right spot. If wrong spot, sorry I'm a newbie to this forum since I just registered today.

Any ways, I got 2 Rainbows yesterday and they were fighting with some of my tetras and those tetras were also fighting back. Then I looked on this sight and I saw that it said Rainbows need at least a 55 Gallon Tank for most of the species. So should I return the Rainbows?

Sounds like a good idea, rainbows do like bigger tanks and the small size might be stressing them and making them nervy. Tetras can sometimes fin nip, and rainbows are what you could call "fin nipper intolerant" In my earlier days , I kept rainbows with tigerbarbs in a bigger tank, and if the tigerbarbs even looked at the shoal of rainbows funny, the biggest rainbows (sepiks or the kutubu's ) would seperate out of the mixed shoal and kick the hell out of the entire tigerbarb shoal. Over time , they did in fact "tame" the tigerbarbs shoal into never fin nipping again. Tiger barbs are persistant, and you can imagine the return persistance of defence it takes to stop them doing that. Rainbows can single out offending fish, and can take the fight directly to them, repeatedly.

Generally rainbows are peaceful, only sparring with themselves and ignoring other species, but if there is a massive size difference, small tetras could find themselves on the menu, and fin nippers will get beaten to death if they dont learn to stop. The bigger species of rainbows come equipped with a 35mph body ram, to be used against miscreants. Thats enough to literally cripple most small fish in one major blow, especially if the rainbow manages to pin the offending fish against a wall or decor. The effect israther like a person being crushed between a wall and an oncoming car. They are dead shots too, they seldom miss if they mean it. Like a guided missile. Take the hint from the biting, cos beyond that , they escalate to body ramming if things dont go their way. They rarely use the ability though, because they are primarily peaceful, when youve seen one use it you suddenly realise just how peaceful they are, because frankly, if they wish to use it, they can kill just about any other fish of equal or lesser size at any time, yet it almost never happens.

Most rainbows are totally peaceful, but certain conditions can set them off. A rainbow that has been attacked will take it really personally, and they dont forget. They have a social system based on dominance, and they will use it on other fish that have attacked them. A non rainbow species will probably not know how to show deference to a rainbow, and that could mean death if its a small species.

Ive seen it lots of times with rainbows, their mentality is like "strike one- i'll let you have that one buddy"

"strike two - you wanna watch that mate"

"strike three- , thats tears it, im gonna do you and your whole family!"

You might also have two rainbows that are males,that will make them aggressive, and since they arent in a true shoal, they will be on the defensive. Rainbows belong in shoals of 6 or more, often happiest when shoal numbers reach over 20. They dont work too well when you only have a couple. Even if you have a male female pair they may beat back other fish when they wish to spawn. They need the shoal dynamic to stay calm.

Basically , take them back, because presumably your tank will be too small to increase their shoal numbers. The big rainbows can cover 8 feet of water in a second when they dash, and they are incessant distance swimmers, so it would be cruel not to give them an aquarium of at least 4 feet, preferably with a little flow.

Rainbows are one of the very best large to medium community
aquarium fish, but that comes proviso to certain prerequisites. Mine never harm smaller fish that arent aggressive with them, even baby angels aand small tetras have been safe with them, but in a 120gal, with a shoal of 40, they wouldnt be aggressive anyway.