Seen that before. As the algae dies, it refertilizes itself and contributes to new growth. It is actually sucking up all of the nutrients that the phyto needs. If you nuke the algae, the same result occurs.

If it were me, and it's not, I would start again next year and nuke the algae before it has time to become an infestation. And, keep nuking it. Fertilize lightly.

The above assumes that you have heavy algae infestation.

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP