How much DE do i put in my filter? and what is wrong with it?

i have a 10 or 12 thousand gallon pool, and i need to know how much DE to put in my proline filter (model #, CW2D-006753). im not sure how much to put in, and i think this may be the reason why when i went to open my pool this year, it pumps hard for a little while, about an hour or less, and then i come back and check it, and its barely pumping the water out. i took it apart and completely cleaned it twice, i have no idea what is going on. if anyone could answer both of these questions (why my filter/pump does this, and how much DE to put in) that would be great, thanks.