These shouldn't be discussion threads..but since we're way off the mark already...
1- Never break the ice with
anything in a Pond, you can easily kill the fish that way.
2- a 100W pond de-icer ring is all you need to keep an opening in the ice. Even if it is already frozen over, just lay it on the ice and it will thaw in that area.
3- your waterfall & pumps should ABSOLUTELT NOT BE ON at this time of year!!! All you are doing is making ALL of the water in the pond even colder. The water at the TOP should be the coldest..and as you go deeper each few inches further down is a few degrees warmer. The fish should be sitting at the bottom where the 'warmest' water is.
4- disconnect the pump from the waterfall and remove it ASAP..if you have any lines that break..just repair them in the spring. It's supposed to warm up this weekend ..you should be able to drain the lines then. I've never 'blown' out my lines and have had a pond here for many, many years. I just use gravity
5- a small airpump..like they use in FW tanks can be hooked up to an airline & airstone . Doing so WILL keep an opening in water ice forms.
Only submerge the airstone a few inches (if you hook it to something heavy & drop it to the bottom of the pump - the same effect of chilling ALL of the water will take place.) You can hook it to anything heavy with a hole in it - that is pond safe - but leave enough airline on the air stone end, so it floats up closer to the surface. Those bricks that have multiple round holes in them are handy for this.
Do be sure to protect the air pump from the elements..my air supply is inside of a vented salt bucket
6- 20 comets in a 400G pond is severely overstocked.
7- a question...can we assume that you have stopped feeding the fish for at least the last month or two?