If you normally don't get much ice, which is what I'm hearing, I would not run a pump at all. Keeping an opening in ice is about letting toxic gases out. This is a problem when an ice cover stays on for weeks. The biggest improvement is always a clean pond. Cleaner = less toxic gas.

The other thing you can do having such a small pond is to build a green house over the pond. With that you may not get any ice, or greatly reduced.

Keeping a pump running has the downside of keeping water colder. I don't know how deep your pond is, but most still ponds will be warmer at the bottom, 39F, while at the surface it can be 32-33F because 39F water is heavier. Mixing the water results in all the water becoming 32-33F or even colder depending on minerals levels.

So it's kind of a choice each ponder has to guess at...reduce gas levels with colder water, or warmer water and risk gas levels. Koi can take both for some amount of time. In very cold climates it's a difficult choice. The choice is easier if you don't get much ice.

No reason to run the TT as the bacteria don't function at cold temps. Plus ice can build on the TT and empty the pond depending on pump location.

The plants should be dealt with depending on each species.

Bigger picture...I don't know the size or number of Goldfish and Koi but it sounds like a lot for 300 gal. Having a TT helps in the summer but you're up against it other months.

Waterbug guy-I have (7) 3 inch goldfish in the 300 gallon and it is 30 inches deep and inground. I thought this would be the warmer pond for the winter. I got the Koi and all their 'stuff' from a guy going to college this summer and had no experience with them. They are way more poopy and ate the plants in the bigger pond so I had to put them back in the one they came with. I built the TT after reading about what they need to keep their home clean. I have 3 butterfly koi that are about 12" and 3 that are 4". I think it is too much fish for the 150 gal. trough but they were in a small tank in his house and that is why I tried to put them in the bigger pond at first. Water lilies-yum yum. I can shift all the plants to the 150 gal pond for the winter and put the fish all together in the bigger pond if this would be better for them during the winter. I just don't want anybody to die. Next spring I am going to try to find some of them a new home.

You really should find a new home for your big koi. The stocking rule of thumb is 300 gallons per koi, and 30-50 gallons per goldfish. Many koi clubs have a "rescue" service for koi that need a pond. If you intend to build a bigger pond for them next year, you could keep the little koi.

I'd run the bubbler, but turn off the tower when you get freezing weather.

A bubbler will be adequate.

My wife has just a aeration device in her 450 gallon tank. She gets no complete coverage with ice until the temperatures drop well below 20oF but here low temperatures are brief, just a few hours before dawn. I can see where local weather behavior could make a considerable difference in what must be done.

I take my koi inside through the winter. I have a 1000 gallon intex pool that I place my pump and filter in. I put it in my basement, not only does it keep my fish growing but keeps their immune system healthy. Healthy Koi need to be in water that is above 70 degrees. I have never had a sick fish and I have been raising Koi for resale for many years. If you have the room I highly suggest it.

Wow, I can't imagine 1000 gallons in the house. I have no space that would accommodate that but it would be neat to have your fish inside with you. I will do the bubbler this winter and find them new homes next spring. I will miss them but I am more comfortable with goldfish.