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Can anyone help me with some Betta fish advice? - floating aerators

I had a Betta fish for 2 years and I have a gallon tank with an aerator .. Bubbles .. , Etc. For some reason, remains on top of the tank. It is not a disease or something, I do not understand. Not dead, but floats. Are you close to death? It is the swimming on the floor .. but can not. What could be the problem? Can anyone help?