What is the Optimum Range of Temperature for Aquaponics?

Last Updated on January 4, 2019

Temperature is a key parameter in aquaponics. As you know, there are three main players in Aquaponics.

  • Plants
  • Fish
  • Bacteria

Water temperature affects all aspects of aquaponic systems. Overall, a general compromise range is 20–30  °C. Temperature has an effect on DO as well as on the toxicity (ionization) of ammonia; high temperatures have less DO and more unionized (toxic) ammonia.

Let’s have a look at how temperature effects!

Temperature effect on Plants

Roots rot in hot Water
Roots in Water having High Temperature

The suitable temperature range for most vegetables is 18–30  °C. However, some vegetables are far more suited to growing in particular conditions.

Many cool weather vegetables such as lettuce, Swiss chard, and cucumbers grow better in temperatures ranging from 8–20  °C. While warm weather vegetables such as okra, Asian cabbages, and basil require temperatures of 17–30 °C. In higher temperatures of 26 °C and above, leafy greens bolt and begin to flower and seed, which makes them bitter and unmarketable.

So the first rule is to make sure that you are growing vegetables according to their season. Season and environment will also have an effect on water of aquaponics system. That can affect the plants’ ability to absorb nutrient and grow.

Controlling water temperature won’t be a big problem for everybody depending on where you’re growing, but for those growing outside or in a hot/cold basement or garage, it will be more difficult because you can’t always control the environment that easily.

Plants grow in soil/ground naturally and ground acts as a natural insulator against the heat.

If you have ever dug a hole more than a foot deep, you’ve seen first hand just how cool and moist it is down there compared to above ground. That’s the environment where the roots naturally live, and the environment they are comfortable in. When the roots are exposed to conditions outside their comfort zone it becomes stressful for the plant.

Generally, it is the water temperature that has the greatest effect on the plants rather than the air temperature.

Problems resulting from High water temps

High water temps will cause heat stress for the plants. At extremely high temps, plant to ultimately shut Roots subjected to high water temperature down and go into survival mode.

Some of the symptoms include

  • wilting
  • causing the plants to abort fruiting and dropping flowers
  • soft and/or brown spots on already existing fruit
  • lettuce plants to start bolting (elongate and go to seed)
  • low dissolved oxygen levels
  • roots beginning to get slimy
  • roots turning black and dying
  • High temperatures can restrict the absorption of calcium in plants.

The severity of the problems will depend on the degree of heat stress your plants are suffering from. This means not just the water temperature but combined with air temperatures and humidity as well.

Problems resulting from cold water temps

While cold nutrient solution temps aren’t that common of a problem, it can be a problem for some people. It’s mostly a problem when growing

  • outside during fall, winter, and/or early spring
  • in a cold garage, basement, root cellar, etc.

Cold reservoir temps really only have one major drawback. Cold temps stunt and slow the plants’ growth. How much depends on how cold the water temps are, and how long they are exposed to it.

You may notice a reduced growth rate when the water temps drop below 60 degrees Fahrenheit (15 Celsius). Since air temperature greatly affects your water/nutrient solution temperatures, cold reservoir temps are usually a result of cold air temperatures. The combination of cold reservoir temps and cold air temps together cause a much slower growth rate combined. Even if the air temps are higher than the water temps during the daytime, the plant will still take much longer to begin waking up because of the cold nighttime temperatures.

Temperature and Fish

Fish are cold-blooded and, therefore, their ability to adjust to a large range of water temperatures is low.

Furthermore, Fish can be categorized in cold water, cool water, and warm water fish. Generally, tropical fish (e.g. tilapia, common carp, catfish) thrive in higher water temperatures of 22–32 °C. However, cold-water fish such as trout prefer 10–18  °C. Meanwhile some temperate water fish have wide ranges, for example, common carp and largemouth bass can tolerate 5–30 °C. You need to consider many factors along with temperature to choose your fish, check this guide to choosing aquaponics fish.

A steady temperature within their correct tolerance range

  • Keeps fish in their optimal conditions
  • Aids fast growth
  • Facilitate and efficient Feed Conversion
  • Reduce the risk of diseases.

The fish appetite is directly related to water temperature, particularly for tropical fish such as tilapia, so remember to adjust or even stop feeding during colder winter months.

Elevated temperatures increase the metabolism, respiration and oxygen demand of fish, approximately doubling the respiration for a 10° C rise in temperature. Hence the demand for oxygen is increased under conditions where oxygen supply is lowered. The solubility of many toxic substances is increased as well as intensified as the temperature rises.

Dissolved oxygen is largely affected by pH, Temperature and water quality. See in details Role of Dissolved Oxygen in Aquaponics

Thermal isolation, water heaters and coolers help to achieve a steady temperature level, although these may be costly in areas where energy is expensive. It is often better to grow fish adapted to local environmental conditions. Each fish has an optimum temperature range that should be researched by the farmer.

Check the best water heaters for Aquaponics here

Nitrifying Bacteria

Water temperature is an important parameter for bacteria, and for aquaponics in general. The ideal temperature range for bacteria growth and productivity is 17–34 °C. The growth rate will decrease by 50% at 64° F (18° C) and by 75% at 46-50° F. No activity will occur at 39° F (4° C). Nitrifying bacteria will die at the temperature below 32° F (0° C). or above 120° F (49° C). Low temperatures have major impacts on unit management during winter.

Aquaponics cycle depends largely on these bacteria. Also, read What are the Water Parameters that affect Aquaponics Cycle

Overlapping Temperature

The optimal temperature for aquaponics is

Fish Temperature = 10-32 °C

Root zone temperature = around 22 °C

Bacteria and Nitrification = 25-30 °C

Overlapping temperature of Plants, Fish and bacteria in Aquaponics

The general temperature range is 20–30  °C, and should be managed in regard to the target fish or plant species cultivated; bacteria thrive throughout this range. It is important to choose appropriate pairings of fish and plant species that match well with the environmental conditions.

If the temperature is too high

  • Some fish will eat more food and hence ammonia/nutrients will increase
  • Higher temperatures diminish the solubility of dissolved oxygen and thus decrease the availability of this essential gas.
  • Plants will begin to wilt and die.

If the temperature is too low:

  • Bacteria will stop working
  • Some fish may not eat
  • Slower Plants growth

Recommendations

  • Carefully choose the right types of plants and fish to meet their optimal water temperature ranges.
  • Choose the plants and fish already adapted to the local climate. However, there are management techniques that can minimize temperature fluctuations and extend the growing season.
  • Shield the water surface itself, in all of the water tanks and units, from the sun using shade structures. Since systems are more productive if the daily, day to night, temperature fluctuations are minimal.
  • Similarly, you can protect the unit thermally by using insulation against cool night temperatures wherever these occur. Alternatively, there are methods to passively heat aquaponic units using greenhouses or solar energy with coiled agricultural pipes, which are most useful when temperatures are lower than 15  °C;
  • Take into consideration the seasons of vegetable while choosing the Fish

 

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