Will he survive? (URGENT EMERGENCY!)

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One of my little baby goldfish is having trouble. He is not swimming effortlessly, like he is supposed to. He's swimming with all his energy it looks like. Everytime he gets near the bottom of the tank, he floats back up. He's alive, I know. But I want to know if I can nurse him back to health in a large tub-o-war contanier, I took him out of his bigger tank because I didn't want him to get his other goldfish friends sick. Will he survive without a filter? And how do I help him? Is there any way anyone knows what his problem is? Thanks and please reply ASAP, this is URGENT!