Acquaplancton pond clarifier
 

Last weekend i mixed with water and decanted a sack of this in my wild pond to reduce algae. I had a thriving shoal of tiny (1-2 cm long) Golden Rudd fry. Three or four hundred probably.
The effect was devastating. Within three days most of them had died.
There was nothing in the instructions to suggest this compound is toxic to really tiny fish. I am very depressed and extremely annoyed.
My guess is that the hungry fry ate it.