Hi and welcome to the forum
Need some better pictures and information about the fish and tank.
How long has the tank been set up for?
What sort of fish are in the tank?
How long have you had the fish for?
What symptoms do the fish have?
What is the ammonia, nitrite, nitrate and pH of the water?
What sort of filter is on the tank?
How often and how do you clean the filter?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the tank?