Trevor I am surprised that the goldfish die during your winters.
It wouldn't be the cold, they can take it a lot colder than anything you would have there.
I wonder if it is an excess of oxygenating weed during the winter?
The oxygenating weed only gives off oxygen during the daylight hours.
It then consumes it during the night hours.
In winter, when the night hours are longer, it would be taking more than it is giving. I remove a lot of my oxygenating weed in the autumn, about two thirds of it.
It could be a different reason why your fish die during the winter, but lack of oxygen could be the cause.
Thank-you Charithea. My garden has to get by with just being watered once a fortnight. As it is closely planted it holds the moisture in, so once a fortnight is sufficient.
The pond needs topping up quite frequently in spring, but now that the water lilies are covering two thirds of the pond surface, the evaporation is a lot less and it only needs topping up now when I do the watering.
Daisy