white bubble on fish fin??

[michypa]

hi my fish (pink glo fish tetra) is over two years old, his fin turned black about a year ago and now he has a clearish bubble on both sides of his top

fin. does anyone know what it is? should i take him out of the tank. i read about air bubble disease which is called by temperature change, etc in the water which is not something that ever happened. i also read that it could be ich which i don't think it is either, i have seen ich before and it doesn't look like that. please let me know. thank you