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Do I need to break the ice on my pond? Not necessarily.
Isn’t ice bad for pond wildlife? Not automatically – its natural for ponds to ice over in cold weather. Pond animals can often tolerate the low oxygen levels you sometimes get under ice. They only get into difficulty when there is no oxygen at all.
What’s the effect of ice on a pond? It can lead to reduced oxygen concentrations – but as I’ve shown over the last few days it can also increase oxygen too. We don’t know how common increased oxygen levels under ice are becuase no-one has studied small ponds carefully enough. In lakes increased oxygen levels, in winter under ice, have been found.
Shouldn’t I make a hole in the ice? You can, but it will barely affect the amount of oxygen in the pond. Oxygen diffuses so slowly into water that making a small hole in the ice will only allow infinitessemally small amounts of oxygen into the pond. Even if you remove all the ice, unless the pond is stirred up in some way, it will make little difference to the amount of oxygen in the water.
Should I float a ball in the pond to stop ice forming? Using a ball to keep open a hole won’t make much difference to the the amount of oxygen in the pond. But it might give the pond an attractive ‘iced-cup-cake-with-a-cherry-on-top’-look. If you really want to increase the oxygen levels, see below.
How can I increase the amount of oxygen in the water? You need to stir the pond so that de-oxygenated water is constantly brought into contact with the air. This is why rivers usually have lots of oxygen dissolved in the water – because they are moving. It’s also why you bubble air into an aquarium.
To add oxygen to water you need to run a pump which constantly stirs the water around, or bubble air vigorously into the pond, or run a fountain which also mixes the water up with the air, allowing oxygen to dissolve much more quickly into the water.
What about fish? Pond fish (like goldfish, crucian carp or tench) can tolerate very low dissolved oxygen levels, especially in cold weather. If you’re worried, you need to keep the water stirred up, which will oxygenate the pond and automatically stop ice from forming.
Can I measure how much oxygen there is in the water? Yes, but dissolved oxygen meters are quite expensive, usually in the £250+ range. But if you’re keen, or have expensive animals in the pond, it could well be worth it.