Dan,
A couple of days ago, I heard of a pond that had got a load of ash in it due to a farmer burning some prunings. The pond owner was annoyed.
The farmer was a well-intentioned chap so, next time, he popped over (the pond owner was out) and covered the ponds with some tarpaulin so no more ash would get in. Most of the fish promptly died. They were poisoned by fire retardant on the tarpaulin.
Check with the manufacturer to make sure you don’t make a similar mistake.