Hello and thank you for your inquiry.
The haze is usually caused by one of two things, salt creep or calcium build up. With a tank full of water it can be very difficult to clean this safely. For calcium build up you will need to find a way to dissolve this from the glass. For empty aquariums the use of some type of acid works well (vinegar or muriatic), but with a full tank it will be a little more difficult. I would suggest trying the use of vinegar on the glass. Drain the tank down some (maybe a 1/4 down) and use papertowels soaked in vinegar to rub over the glass. Hopefully with enough elbow grease and the power of the vinegar it will help remove the haze.
You can also try using a sharp blade (razor blade), but you will need to be extra careful.
If there is anything else we can do for you please let us know.
Marine Depot Customer Service