AJ, welcome to the forum. I'm almost positive that Dave is correct in his assesment, algae will clog a de filter very quickly (the reason being that individual algae cells are ~the same size as the filtering channels in the de). However, the grids may have accumulated oils or calcium build up over the course of 7 years, in which case a TSP bath and an acid bath may be in order.
Do you have sufficient water, both in the pool and available to refill the pool, to do your vacuuming to WASTE ?(no relation to me) As Dave said, getting rid of the algae should be your priority. If you need any help with the algae removal, take a look at the "Dealing with algae" section of this forum. Good luck and keep us posted - should you need any more help, just ask, some of us live for this stuff