Last couple years I have had a diffuser with 4 air stones on it running thru the winter under my dock. This summer I added a 2nd diffuser that same setup out in the middle of the pond and ran it all summer.

Soooo now here we are in winter...
The diffuser at the dock is fine, it has a large area with open water working great. The new diffuser in the middle had a hole of open water but I had turned the system off for a few days and turned it on again now there isn't a hole of open water in the middle.
I am wondering if this a bad thing to have this run under the ice?
The diffuser is at about 8 feet of depth that isn't creating open water where as the dock diffuser is at about 4 feet.

Thoughts would be great.
Thanks in advance.