Is the material a soft yellow? If so, you may be confusing pollen with a precipitate. Our evergreens here in NJ put out a pollen exactly like you describe, but I usually only see it in the spring where it coats my skimmer socks like crazy--just like spackle. If I see anything the rest of the year it's whitish-grey.

I'm not the expert on sequestering agents, which should only be used when you are PROVEN to have excessive metals, but my understanding is they are supposed to dissolve and suspend the metals, not precipitate them out. Are you also using something like a flocculent agent?