If the chlorine is holding pretty good, you might be at the stage where a little DE added to your sand filter would clear things up. Just be sure you do it when you;re around to babysit, because people have reported major pressure increases within hours after adding. You want to be there to keep an eye on it so you can backwash when needed.
My pressure does not drop real quick with back washing, but I will try it. Should I add the 1/4 cup mixed with water or go with 1/8 cup mixed with water