Oxygen in ponds

but you don't need them in wildlife ponds

Fountains add oxygen to the water: but you don't need to add oxygen to wildlife ponds. Instead make sure the pond isn't polluted

Most advice about looking after ponds repeats the old idea that well-oxygenated water is vital for a healthy pond.

But is this true?

Oxygen levels naturally vary in ponds – higher in cold weather, lower in warm, higher during the day, lower at night, higher in ponds with a sandy bottom, lower in ponds with lots of oxygen absorbing plant debris. Water plants, including microscopic algae, also cause big fluctuations: in the light they produce oxygen while at night they use it up.

Rivers and streams, on the other hand, have pretty constant and high disssolved oxygen levels, mainly because their flow constantly mixes oxygen from the air into the water.

Animals living in freshwater have adapted to these natural differences over the millenia. Pond animals often get their oxygen from the air, coming to the surface to breathe. If they live permanently under water they usually tolerate occasional low oxygen levels, like pond olive mayflies.

So does adding ‘oxygenating’ plants make any difference? Not really, because although they produce oxygen during the day, they use it up when the lights go out. They might just as well be called deoxygenators.

Unless you are keeping a lot of oxygen demanding fish, you don’t need to add oxygen to your pond. And if you do, its probably better to get a fountain.  Plants are just as likely to kill your fish by using up all their oxygen in the night – something a fountain won’t do.

But plants are beneficial: they provide vital cover, habitat and food. And they look good too.

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