How many plumes do you really need to give the fish a warm water refuge with oxygen? Since you can run a big system and use 4 diffusers at a time, if you took down the little bubblers or the windmills and just ran one big hole or two big holes (maybe one more shallow and one where the hole is now) wouldn't that be enough to keep the fish alive for the winter? Or do you need multiple holes all over the place?