Correct me if I’m wrong, but chlorine being a very strong oxidizer will break down quickly and react with any organic matter. If the pond basin is thick muck, it is questionable how long the active chlorine will last to provide a lethal dose to the fish. I would suspect you will need to apply a lot more chlorine than just what it takes to get just the water up to the lethal level. I would also suspect you wouldn’t want to be anywhere near the treated pond for a few days to avoid the out gassing which is going to be quite unpleasant, if not caustic to your lungs and nose.
If you manage to drain the pond sufficiently, think of the treated area as a burn scar, as that is what it is. But the banks of the pond that are untreated should still hold plenty of organisms to seed the pond fairly quickly when it refills. Just treat it like a freshly dug pond, starting with a forage base the first year.
