I doubt you'll open up enough water to create superchill conditions. I've been running my diffusers in my ponds 24/7 all winter and they only open up about 5 percent of the surface area. The pond we talked about where the early spring snowstorm killed some fish was wide open before the snowstorm hit and they got 21 inches of heavy wet snow in a very short amount of time.
I think you'll be O.K.
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
