These two adjectives have different meanings.
Turbid means unclear, foggy, cloudy, murky, or, in other words, like dirty water, or smoky air.
Turgid means swollen, over-full, and metaphorically—pompous.
Turbid can describe cloudy air or water or be used metaphorically:
We couldn’t see any fish in the turbid lake.
It was difficult to understand his turbid writing.
Turgid can mean “physically swollen,” or metaphorically describe pompous language—language which with unnecessarily big words, complex syntax, and long sentences:
After the snake-bite, Mike’s arm became turgid with fluids.
It was painful to read the bureaucrat’s turgid writing.