Pond Boss Forums INTRO Questions & Observations Fish Kill,,,Assessing the damage and moving on

I feel for you. It's so frustrating to do everything correctly, then be rewarded with a kill.
The problem is related to your water. Planktonic algae is certainly an issue, as was treating too much algae in the first place.
But the answer may lie in something we don't obviously see.
Had your pond been fertilized? It sure seems as though there were/are too many nutrients being taken up by too many/too much plant mass.
While the after effects of the treatment may have caused the fish kill, it may not have been the problem.
Follow the nutrients, and you will find the problem.
Was the pond fertilized? Heavily fed? Lots of livestock feeding, wading, pooping? Other sources of nutrients? If so, that's the issue. If not, improper techniques for treating, and mis-reading the resulting plankton bloom are the problems.