The white/ grey film spreading over the electric yellow cichlid is excess mucous. The fish has clamped fins and this combined with the excess mucous would suggest it has a protozoan infection or the water quality is really bad, most likely the former tho.
Have you tested the aquarium water for ammonia, nitrite, nitrate, pH & GH?
If yes, what were the results?
How often do you do water changes and gravel cleans, and how much water do you change?
How often do you clean the filter and how do you clean it?
Have you added any new fish within a month of this showing up?