I hate to tell you this but diffusers are lousy aerators in an emergency. That's not their purpose. You need some suface agitation pronto. Sweeper nozzle, trash pump shooting water over the surface whatever. Here's a good publication on various types of pond aeration. Granted it's related to commerical aquaculture but it has some good information.

http://aquanic.org/publicat/usda_rac/efs/srac/371fs.pdf

A word to the wise. Whenever you are doing a significant weed treatment it is a good idea to have a surface aerator handy or in use in case D.O's plumet.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.