Yes, they are the best choice that I have found for running pump all winter, cause they are very large and you can connect additional filters to make it even bigger. During the middle of the winter you really need a good size underwater pre pump filter that will not clog up or slow down the flow of water from hose. If the pumps get clogged, then the volume of water coming out of hose slows down too much, and then that can cause the hose to freeze if very cold. Same trouble with external box type filters, too much water pressure is lost inside the box, (as water goes from small hose to large filter style box, water pressure drops too much) and that can cause the box to freeze too.
The "pro pond guy" in town, who has a huge six foot deep pond, and he installs ponds all with the same setup, skimmer that draws water from pond and pumps up to a large box type filter that feeds some stream, operates his pond all winter, but shuts down pumps and external filter, and just runs a big air pump and heater, and last winter he lost many of his large koi when spring came. Air pumps or aerators, just do not cut it when extreme cold sets in. Trouble with air pumps is that they too can condensate and freeze up too cause the line is above ground. Then air pumps just cause bubbles to make even more thicker ice on top of pond as the bubbles spit tiny water droplets on ice that just freeze and create thicker ice, If you live in a zone that is not so cold, and if you just have smaller fish, then less trouble as smaller fish require less oxygen, and air pumps fine for warmer zones. If you have really big koi like me, and really harsh winters, then you need to insure that the harmful gases that build up under the ice are carried away, and not trapped under some thick "dome" of ice created by a air pump. I have run my pumps all winter with the big internal filters and internal pumps for over twenty years now, and have seen many pond friends with big koi that only had heater and air pumps, and they all have suffered large losses of fish during winter, at some point, Sometimes they can get away with it for a couple seasons, but as the koi grow then more problems wintering as they run out of oxygen and die off first and then they are left with just the smaller goldfish. I have seen this for many years and have warned about running just air pumps in extreme cold for a very long time.
My method has worked very good over the years with little trouble. I have three fair size ponds that are all connected to each other with little water ways that run water from top pond, free flows thru middle pond, and down to bottom pond. Upper ponds have the least ice, and they de- ice very quick cause the "running" water melts ice very quick, and so I keep the biggest koi in the upper pond, as that pond has the freshest water and gets the least amount of ice. It is complicated to explain, so I have made many videos and they are posted on this thread last winter. I will take more videos all winter of my pond system and try my best to explain why my way of wintering works best for extreme cold.
The simple explanation is "my ponds run like a river, stream or creek, where the water is always flowing, from top pond down to bottom pond, and a river, creek or stream, the ice melts way way faster in the spring than a lake does, as the water in a lake does not move much and so the ice is way thicker and you can drive a truck over the lake ice in the winter. Streams and rivers are more likely to have thin ice in many spots where the water moves quicker. and the thin ice has many natural breathing holes created by faster currents, like all rivers and streams do. These holes provide a way for built up gases to escape and oxygen to flow more freely.
Coming soon to this thread... {hopefully not too soon!! ha ha ha} Winter and weekly videos on how my pond operates in minus 40 degree weather!!!
In the mean time I am going back to play outside with my Halloween stuff and sit in the nice cosy
Haunted Gazebo!!