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His left eye looks cloudy and grayish, some skin shedding around this eye lid. I compared to his right eye which looks black and shiny. He blinks his sick eye more often and once in a while he shut that eye for some time. But most of time he doesn't seem to be bothered by that eye. I think I am gonna skip the detail description about his living conditions, I would say everything is normal, 78 degrees temp, both lights, and he eats a lot and swims a lot, looks totally healthy otherwise.......

I would take him to the vet
The symptoms most likely show an eye infection
If you have other turtles in the tank seprate the sick one
cuz the others could catch it

The vet could give you eyedrops and certain care procedures

Perhaps pick up some turtle eye-drops (honestly not sure where to find them). He might have just scratched his eye, or perhaps it's to do with one of the lights (though it'd be strange to have only one eye affected).

Keep a close watch on it, though.

by the way, its been 2 months and it's not been any worse or better

Two months? That's a good long while. Could you perhaps post some pictures of your turtle for a closer look?

will do tomorrow...thx

I'd take the turtle to a herp vet and have the eye swabbed for a culture.