If your pump sat in sub-freezing temperatures with water in it, it is probably permanently damaged. I run my pump and waterfall all winter and I would never let it go off. If my pump were to fail, I'd disconnect it and bring it inside straight away. Pumps, or even pipes for that matter, should never have water in them when the temperatures fall below freezing. That is, unless the water is constantly moving.

I don't think that counts if you have a submerged pump. You don't say what your set up is. I have had to leave mine submerged without running it several times without damage through the winter because I couldn't pull it in time. Of course that could be a fluke. The water temps are not as severe as the air temps. We have decided to let the pump continue again this winter. We like the sound.

I would suppose it would depend on how noisy your pump is when it starts. I don't think it would improve the quality much if it is going through the same uncleaned filter material if you have a Skippy. It might make it worse. If I added anything it would be another bubbler.

Remember, there could be ice in the pipes if they are exposed to the air. I have had sleepless nights when the temps were really low thinking that might happen but I guess the pump is moving enough water to prevent that. I doubt we will get lower than 8oF but if it happens I will put some sort of cowl around that short section.

We are expecting the same temperature bump. I doubt I will make any changes at this point, unless I replace the filter material. The waterfall has been going even in the sub-freezing temperatures we have had without stopping. The water is coming through a pipe of ice that formed around it. The bubbler has managed to keep a hole open except for about 12 hours at 8 degrees ambient but that ice broke up quickly. Where there is less water coming to the top, the ice is several inches thick.

The birds and squirrels have been drinking at the Skippy instead of trusting the pond ice that thins considerably around the bubbler. That makes me a lot less nervous about broken ice and rescuing the critters in this cold weather.