I do know once the ice is thick enough it's tough to get the upwelling water to cut it. Don't ask me how I know.
I didn't have too many issues with the big pond installing a diffuser and keeping water open after the ice formed, as I think there is relatively more warmer water reserve in the depths. Also the hole started out big enough for the wind to aid in keeping it open.
Different story in the smaller trout pond that is more protected from the wind and freezes sooner and deeper.
