Don't clean your sandbed. The only time that you want to disturb it at all is if you need to suck up a cyano
outbreak...which then you want to suck the cyano
up, not the sand.
Carbon should be polishing the water for you, basically. Are you sure the 'white' effect isn't reflection from the white arches and such you have in your tank? That is all you can see in the picture.
In terms of feeding, you should feed sparingly. I feed my 55 reef tank half a cube of mysis every 3 days. You don't want excess food floating around. What you put into the tank you need to remove. This is one reason we do water changes, to take the nitrate/phosphates out. The media you can run will absorb some of this, but not all.