Help! My sick betta is getting worse :/?

My black skirt tetra has the same thing.Although i have medicine(Quick cure,works really well)for my fish,i decided to let it be and see if it would heel or not.It hasn't really at all.But then again,he is a black Skirt tetra. Maybe you should try a small water change,don't forget to add water conditioner.If you feel your betta wants more rest or more darkness,then you could buy a small ornament that he could swim into to get away from light.Best of luck!!!