Oh, how very frustrating!

I'm no expert with DE filters but what I would do at this point is to set it to recirculate rather than filter and keep shock levels up, 24/7. Brush before you add bleach and brush again after you've added it to get as much algae exposed to the chlorine as possible. The water will eventually turn a cloudy blue. Our DE filter people will be able to advise you how to manage the filter.