Beat the heat
At this time of year you can spend long, warm evenings enjoying your pond fish, which are at their most active right now. But rising temperatures can cause problems. Here’s how to prevent them.
Summer temperatures can cause problems for pond fish. Here’s how to prevent them.
After bringing your pond through the delicate spring period, summer is the time to lie back and appreciate your hard work. However, there are several unique problems that can arise in pond water at this time of year.
Warm water worries
One of the properties of water is that as it cools down it can hold more dissolved oxygen. A sample of freshwater at 5°C is saturated with oxygen at 12.76 mg/l. However, a sample of water at 25°C is saturated when it holds only 8.24 mg/l of oxygen.
So, what are the implications of this for our pond? Firstly, there is less oxygen available to the fish when the water is warmer, but to exacerbate the situation the fish become more active at higher temperatures, meaning they have a greater demand for oxygen. For every 10°C rise in temperature the metabolic rate of the fish roughly doubles.
It is not only the fish that will have a greater oxygen demand, the activity of the filter bacteria is also dictated by temperature — the warmer the water the faster they metabolise. Couple this with a greater production of ammonia by the fish, and the increased overall consumption of oxygen by living organisms in the pond, the amount of oxygen available is at an annual low.
To manage this summer oxygen paradox, it is essential to ensure that the water is thoroughly oxygenated throughout the summer. The best way to do this is to use a test kit to analyse the oxygen level to ensure it remains at a value that can meet the requirements of fish and filter bacteria.
Oxygen concentration can be expressed in mg/l (or the similar expression; ppm), but this fails to account for the saturation value of oxygen in the water. A more convenient expression is percentage saturation. For example, freshwater at 25°C holds 8.24 mg/l of oxygen at 100% saturation, if the level dropped to 6 mg/l then the sample would be 72.8 % saturation.
As such, during the summer months you need to be especially vigilant of dissolved oxygen levels in the pond. Regular testing is useful, thorough aeration of the water by airstones, venturis, waterfalls and/or fountains is essential. During especially hot and humid days, the dissolved oxygen level can be at its lowest — always make sure you have hit a minimum of 60% saturation but strive for a value nearer to 80%. The closer biofiltration chambers are to saturation with dissolved oxygen the better they function.
The dangers of algae blooms
Another problem that can arise in ponds in the summer is blooms in the growth of unsightly blanketweed and green water algae. These primitive plants have basic requirements including dissolved nutrients such as nitrate and phosphate and sunlight to allow them to photosynthesise. In many ponds algae becomes a real problem in the summer as the sunlight reaches the correct intensity and shines for a sufficiently long period of time to allow algal growth to proceed at a maximal rate. Tetra Pond Algofin and Algorem can help to safely and effectively treat algae problems. Apart from looking unsightly, algae can cause numerous water quality based problems. On a basic level, algal cells and strands of blanketweed soon clog filtration systems, meaning you’ll need to carry out more routine maintenance to keep the life support system of the pond running efficiently.
Down at a chemical level the pond water is being profoundly influenced by the growth of algae. The photosynthetic processes which occur only in daylight hours, sees the liberation of oxygen and the uptake of carbon dioxide. These processes occur at the same time as the normal respiration of the plant, but there is an overall increase in oxygen and decrease in carbon dioxide in a pond with heavy growths of plant life.
At night photosynthesis stops, but respiration continues leading to a decrease in oxygen levels and increase in carbon dioxide, a trend that continues until sunrise.
How does this affect the fish?
Firstly, the oxygen level in the pond will be far from stable, lakes heavily choked with algal growth have been recorded fluctuating from a supersaturated 169% down to a low of 39%. Such instability causes chronic stress to fish and would need to be remedied.
Another problem is the carbon dioxide release which increases at night. The chemistry of carbon dioxide in water is very complex, but can generally be considered to lower the ph as it leads to the formation of carbonic acid, meaning that more carbon dioxide leads to a lower ph.
The ph is held stable by the buffering system or carbonate hardness (KH) in the water. Ponds with a good strong KH (>6 °H) can resist the change in ph for a decent length of time, as the KH can buffer the carbonic acid. Remember though that KH can become exhausted and is best replaced by a water change with hard to moderately hard water. If you live in a soft water area of the country then KH can be raised by placing cockle or oyster shell into the final stage of the filtration system. Alternatively, you can improve water quality by adding Tetra Pond Water Balance which helps to maintain the correct water conditions, stabilising ph and KH to promote a healthier pond environment.
So, you can see that a pond choked with algae is a potentially dangerous environment for the pond as well as an eyesore.
The action plan involves getting rid of the algae, ensuring the oxygen level is not fluctuating by vigorously aerating the water, especially at night, and finally ensuring the pond is not suffering daily fluctuations in ph by maintaining a good level of KH in the pond water.
Summer is the time to get out and relax by your pond — but are your fish as happy to see the warm weather as you are?
Summer blanketweed isn’t just unsightly — it could lead to a wipe out in your pond!
Widely fluctuating oxygen levels are highly stressful for your fish.