In this article we talked about the importance of the light and learn how much light to give to your tank (where to place it inside your house), and why in some instances the light can damage your culture.

Here I’d like to introduce a very unique mechanism, super useful to know for growing spirulina at home, called the “auto-shading mechanism”.

What is spirulina auto-shading mechanism?

The auto-shading mechanism comes from the Greek root αὐτός – autós: self / same, and it’s basically, the ability of spirulina filaments to shade each other.

How does it work?

When spirulina cultures start, there aren’t many spirulina filaments in the tank or pond. This means that each filament will be exposed to a lot of sunlight. As spirulina cells become denser, the filaments on top of the culture will shade the other ones lower in the water column. Spirulina can also change forms as a response to light intensity and go from the usual spiral form to a straight filament and vice and versa, to chance the amount of light or shade that goes down the water column. 
straight spirulina with logo

Is it important when growing spirulina at home?

Yes it is! Very much so. If you grow spirulina at home, this is something you want to avoid. Harvesting straight spirulina is much more difficult because the straight spirulina won’t go through the filters as well as the normal form and you’ll end up breaking the cells and loosing a lot of your production.

So what to do?

  1. When you start your culture and there’s only a few filaments, or when you just harvested, (check the image on the left on the illustration here under), you have to protect your spirulina from the damages of too much sun and shade the tank. You can use bamboos or an agricultural cloth.
  2. As the spirulina grow, you’ll have more and more filaments that will shade and protect each others and you can slowly increase the sun exposure. However, you will need to have some agitation or aeration in the culture to allow a good circulation of the filaments in the water column, because you don’t want the same guys to always be bombarded by the UV light!
  3. When the culture is dense enough, with a Secchi disc reading of 3 cm or less, spirulina will shade each other enough and you don’t need to have any other type of shading on your tank. Here the agitation of the water column is crucial because the light won’t penetrate as deep and you need to make sure the spirulina filaments that are on the bottom of the water column also get some light (=get to the surface of the aquarium) so you will have to increase the agitation to make sure that every filament of spirulina gets just the right balance of light and shade to grow and thrive. Once you have reach that stage, the production will increase with an increase of sunlight, up to the point of photolysis.

How to be sure?

Most of the time you can eyeball the state of your spirulina.

If you see that the spirulina is growing well, continue to reduce the shading progressively.

If you see that you go backwards (the Secchi reading is increasing), you might need to add some shading, especially if you live under the tropic.

For the geeks out there (like me 😉 ), light can be measured by a photometer, super easy to use and for a reasonable price to! I recommend this Luxmeter. Or you can make one yourself.

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