What's the diameter of your pond - 15 feet or so? It seems that you had way too many fish that your pond could safely support. I think the deaths can be attributed to the overcrowding, not the weather. It was just a matter of time. A friend of mine is a biochemist and did an experiment with a fish tank ... he kept adding fish to see how many the tank could handle. Unfortunately he had no warning of anything dire until they all up and died one day. Nature took it upon herself to remedy the problem. Too many fish create too much waste which leads unhealthy water quality which leads to disease and ... dead and sick fish.

I copied this off a UK website (since you are more familiar with the metric system) as an estimate on how many fish a pond can safely handle. Hope it helps. Sorry you lost your fish.

HOW MANY FISH?

To assess how many fish your pond will support, estimate its surface area and allow 60sq cm of surface for every 1 cm of fish (equivalent to 24 sq. inches per inch of fish). Since fish grow and breed, it is best to start off with around one-third of the theoretical maximum number. For example, a 1.8 x 1.2m (6ft x 4ft) pond will, in theory, support 360cm (144ins) of fish, equivalent to 36 individuals averaging 10cm (4ins)long, but, in practice, you should have only about 12.

Golden Rule - Your pond needs to have part of the area at least 60cm deep for goldfish and 1.5m or more for Koi if they are to be left over winter safely in the pond.

Thanks very much for your advice . I've worked it out that really all I can have is about 70 goldfish - a lot different than 225! There are only two fish hanging on at the moment , and I would say that in the next day or two they will be gone. What I will do when they are all gone is clean the pond out and start again from scratch Thanks again .But I think I will leave that till later on in the Spring

Hey there, Garry. Just a thought, do you test the water for ammonia, nitrates, nitrites, etc? That could avoid problems expecially if there is overcrowding. Sandy