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Pond Oxygen Levels: The Danger in Summer

9th April

Keeping the correct pond water parameters is important year around but when it comes to summer, more care has to be taken to keep your pond in good condition. In fact…

Pond fish deaths occur most often between late July and early August.

This is due to the increased environmental effects that summer weather can have on the state of the pond water such as oxygen levels and in turn the livelihood of the fish that live there.

It might be surprising for some to know that fish actually require a certain amount of oxygen to live.

Fish use their gills to filter oxygen out of the water, which is conveniently already present in a dissolved state, making it easier for them to utilise.

However, as fish mature and increase in size, they are less able to utilise the oxygen available efficiently. Therefore, bigger and older fish are more susceptible to stress and death, along with highly selected breeds.

How does the season affect pond oxygen levels?

The warm weather that comes in summer contributes to an increase in pond water temperatures. The problem is that warm water tends to have a lower level of dissolved oxygen than cold water, meaning fish struggle to get enough oxygen, which in turn can potentially cause them to suffocate and die.

While the solution might seem as simple as keeping the water temperatures down, the problem isn’t as straightforward as that. In summer, pond owners can also expect to see rapid growth in algae, coupled with continuous changes in pH levels.

More algae, less oxygen and fluctuating pH levels

Algae is an aquatic plant organism that blooms like we would expect all other plants to in the summer season. In the daytime, algae produce and release oxygen through photosynthesis, however, during night time or even cloudy weather, the low sunlight levels cause algae to stop the process of photosynthesis and instead respire, thereby consuming rather than releasing the already low oxygen levels in the warm pond water needed by fish and instead, release carbon dioxide.

This changing balance of carbon dioxide and oxygen results in a pond that has a continuously fluctuating pH.

The water becomes more acidic when the oxygen levels slightly rise (although still not quite adequate enough) and become more alkaline when carbon dioxide increases.

All of this can be demonstrated by conducting a simple test with a pH test kit at different intervals in the day. The best time to do so would be in the morning and at dusk.

The regularly spikes in pH and overall low levels of dissolved oxygen are a leading cause of fish stress in summer.

Pond owners might even notice that their fish swim to the surface gasping for oxygen during particular times of the day. This most commonly happens early in the morning as this is when algae are likely to release oxygen again.

The solution is to prevent algae from recurring

So now you’re probably thinking what actually causes algae so you can put a stop to it. One source is the naturally occurring nutrients that encourage algae to grow, like phosphates, which are produced from fish waste. However unless you’re planning to get rid of your fish, nutrients like this are probably unavoidable. As mentioned earlier, algae is a form of a plant, so sunlight exposure will also promote its growth, something also out of your control.

Make sure fish have enough oxygen in summer

Fortunately, Algae Klear Xtra targets submerged algae and works to remove algae from your pond but also has the added benefit of a UV filter that blocks sunlight, essentially suffocating the algae’s natural growth process and preventing new growth.

By removing algae and preventing the occurrence of new growth in its peak season, you can remove the risk of fluctuating oxygen levels during a sensitive time and ensure your fish have a better chance of getting an adequate amount. Your fish can safely enjoy the warm weather too!

Also, by using a pond water buffering system such as Pond Equaliser, you not only protect the pond and fish from the pH spikes caused by algae but from other causes on pond water parameters imbalance. For example, fish themselves make the water environment acidic through waste produced by processes of their natural metabolism.

TIP: Don’t overfeed fish in the summer, because the more waste they produce, the higher the risk is for acidic water.

front view of Envii Algae Klear Xtra eliminates submerged algae

Do you have blanketweed? 

Blanket weed is a type of algae that floats at the surface of your pond, also affecting the oxygen levels, discover How to Get Rid of Blanket Weed and how it should be treated slightly differently.

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Geoff Collins

This article is very helpful. I sometimes experience a growth in algae but regularly remove it as best I can. I have used ‘Algae Klerk Xtra’ but found it did not work as expected. In response to this I doubled the suggested dose, this also did not appear to do much, if anything.
I made a purpose made tool for removing the algae and this at least keeps the growth down to a reasonable level. I cannot remove the algae that grows among the ponds plants but at least the water is clear and I can see the fish happily swimming around.