The Hydrated lime is most effective when mixed and dissolved, then sprayed onto the entire pond basin. Many fish can survive in the loose mud and as FireIsHot said, in the little puddles all over.
Broadcast spreading will work, but can take as much as 4 times the H lime than it does by spraying a dissolved solution.
My guess is that the 50# killed some fish, but it's very doubtful it raised the pH high enough to get anywhere near all fish.
Draining a muddy 1/3 acre pond filled with Koi. A total of 600 pounds of Hydrated lime was used on the pond to ensure a 100% kill of everything in the pond's basin.
You can see a few small dead Koi...Larger Koi were netted out and returned to sender before treating...
After treating, the pond was refilled with well water and could have been safely restocked in 2 weeks...
