what kind of fish do you have? what are your tank parameters? what other critters do you have in your tank? with out knowing this information I would guess that one of your parameters are off and a water change is in order.
with this info I would look at your ammonia and chlorine levels both are toxic to fish and can cause the kind of bubbles I understand you to be suffering from. if ammonia is the issue i would recommend a large water change 50% to 80% and treating tank with a water conditioner. If it is chlorine I would recommend a dechlorinating water conditioner as treatment.
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