Why is my 60 galloon fish tank cloudy?

My tank is cloudy and I don't know how to stabilize it. I can't even see my fish unless they are in the front. I have changed the filter cartridge( I have a penguin 350) I did a 50% water change and vacuumed the gravel. What else can I do to clear out the cloudiness? I have my tank set up by a window, Could this be a factor?