Question
Mr. Nesfield,

    My grandfather installed a koi pond two years ago. He never had a fish die untill he put some sponges in the filters(he read that this would help with the algie) a few hours later every one of his fish died. We were wondering since before his fish died they were at the surface gasping for air, what the fish died from.

                          Thank you for helping
                                   Cory  

Answer
Hi,
I am very sorry to hear of your grandfathers koi dying,
it looks very much like they where poisened what had the sponges been used for previously to putting them in the filter because they sounds a bit suspect, the koi would be gasping at the surface for air because of a lack of oxygen in the water.
George.