The temperature will directly influence the growth rate (or growth speed) of your spirulina. And in does so pretty drastically.

We’ve talked in this post about  the four key factors to growing spirulina – the light, the temperature, the agitation and the culture medium.

In PART I  we’ve detailed the optimum light that was necessary to grow your spirulina, and the options you had to place your aquarium in the direct sunlight or use artificial lights. We’ve also seen the different pigments in spirulina and their role in “capturing” the sun energy.

Now you know where to place your aquarium for optimum sunlight (see PART I – The Light) the next key factor is the temperature. Spirulina grows in the wild in tropical lakes. These lakes have relative high-temperature year round. Spirulina will, therefore, need the same range of temperature to thrive in your aquarium.

For example, at 64ºF (18ºC) the growth rate is only about 50% of the growth rate at 68ºF (20ºC)! At 68ºF (20ºC) the growth rate is only 55% of the growth speed at 72ºF (22ºC)! And between 72º F and 89ºF (22ºC and 32ºC) the grow rate double! However, from 89º to 95ºF (32º to 35ºC) the growth rate is about the same, but above 98ºC (37ºC) if you leave the spirulina for too long you will risk damaging it. And it above 110ºF (44ºC) for several hours you will almost certainly kill the spirulina. Ok, that’s a lot of number, but just look at the graph to understand better!


On the other side of the temperature scale, spirulina can survive pretty cold temperature down to 37-41ºF (3-5ºC). But it will only start growing when the temperature is over 52 – 59ºF (14 – 15ºC) and have an appreciable growth over 64ºF (18ºC).

Spirulina grow Rate - temperature

The optimum temperature for maximal growth is 95º- 98ºF (35 – 37ºC).

If you are located in a very hot area, monitor your aquarium, especially if it is placed outside of the house. You can purchase waterproof thermometer at your local pet/aquarium store. You can also decide to invest just a little bit more and by a thermometer that will allow you to also monitor the pH (this is very important – see PART IV – The Culture Medium).

pH meter for spirulina
pH meter/ thermometer

I would recommend to shade your aquarium or pound with a material that will let some light go through like a bamboo mat or an agricultural cloth. Shading of up to half of your aquarium or pond will not really have an impact on your productivity (= the amount of spirulina that you will be able to harvest). Over 50% of shading and the productivity will decrease rapidly.

So if every day you have to shade the aquarium for more than 50%, it means that you have to find a better location. Try the other side of the house, or get a bigger aquarium. If you have a larger volume of water it will take longer for the sun to warm it up. You can do this little experiment to test this by your self.

Place a small glass of cold water in the sun and just next to it place a 5-gallon jar of cold water. Make sure they have the same temperature when you start the experiment. Leave the two containers for 1 h in the sun and check their temperature. What do you measure? (You don’t need a thermometer, you should be able to notice the difference just by testing the temperature with your finger or you can even drink the water to test the temperature – but make sure you cover the glass when you leave it outside in the sun then, you don’t want flies or other insects to go into it!). Well as you have guessed, the large container, the 5-gallon jar is much cooler than the glass. This is called the buffer effect. It’s just like if you put one spoon of sugar in a glass or in the same 5-gallon jar, it won’t have the same effect because of the buffer effect.

So more water in your tank means that the temperature variation will be less.

But in any cases try to NOT have the temperature of your aquarium/pond go over 104ºF (40ºC).

If you live in a cold area or if you keep your spirulina inside and the AC is cranking, you will have to place an electric heater in the aquarium. Turn the heater to 95º- 98ºF (35 – 37ºC) for optimum growth.


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