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Spirulina Growing

In most cases, a Spirulina site is started with a small portion of fresh and mature Spirulina culture. This initial quantity is gradually increased until the desirable quantity is reached.


  • Agitation - Spirulina is a photosynthesizing organism. It tends to gather at the top of the pool or container, where exposure to light is maximal. This means that Spirulina that cannot reach the top will die. In order to enable all of the Spirulina exposure to light, the culture needs to be agitated - either constantly (with a pump or paddle wheel) or manually (with a stick or broom). If using a manual devise it is important to clean it before and after each use. Manual agitation should be done in gentle but thorough circular motions, maintaining the same direction, every 2-3 hours (during the day, when there is light).

  • Light - Spirulina needs sunlight. Having said that, it is important to note that during the first week or so, when the Spirulina is not yet dense as well as immediately after harvest or increasing quantity, exposure to direct sunlight should be limited, especially strong sunlight during the hours that it is direct. During rainy seasons or in colder climates it is possible to provide the Spirulina with the light it requires artificially, though this is less energy and economically efficient. Light that is used in greenhouses that grow flowers is suitable. 

  • Culture level - Spirulina grows in water and it is important to maintain culture level and to add water to compensate for evaporation. This can be done using a ruler (that should be cleaned before and after each use). It is important that the culture be still when depth is measured so make sure to wait a few minutes after agitation (if done manually) or after turning off pump or paddle wheel (if automated, but remember to turn it back on after taking measurement).

  • Temperature - Optimal temperature for Spirulina is 30-35c. Spirulina can survive lower (not below 20c) and slightly higher temperatures (up to 38c), but it is not advisable as its metabolism will be harmed and it may suffer from a state of 'shock'. Temperatures can be measured with a thermometer.

  • pH level – Spirulina can live in a pH level that ranges 8 to 11, but it is at its best at 10.5-11., which is the level that needs to be maintained, as bellow 10.5 it is at risk of being contaminated and over 11 it undergoes chemical changes.

  • Light - There are several devices for measuring level of radiation. A Lux meter is a simple and relatively cheap option. When using this device it is held over a set point (make sure that it is always the same one) on the rim of the pool or container. Make sure it is steady and that the person taking the measurement dose not cast shade over the device. Comparing radiation levels to status of Spirulina (amount harvested, for example) is a good way to learn about optimal ranges. This information is useful for controlling some of the environment, for instance: If radiation level is too high shade can be provided and vice versa, if radiation is too low greenhouse can be opened or artificial light added.

  • Salinity - Salinity is a good indication of culture status. Healthy salinity ranges between 15 to 20 PPT. Several devices can be used. A refractometer is a simple and relatively cheap option (its measurements are digital and a healthy range is between 1 to 2).

  • Density - Amount of light that passed through the culture gives a good indication to the density of it, indicating if it is ready for harvest (or for increasing its amount) or if density is dangerously low. There are several ways to estimate density: Color of the culture - the darker green the culture the denser it is. A second option is looking at a sample from the culture in the microscope - the number of Spirulina filaments and their proximity to one another is a good indication to the culture density. A third option  - an X is written on a white sheet of paper. A transparent graduated cylinder is placed over the X. Spirulina culture is poured into the cylinder until the X is no longer visible from the top of the cylinder. The higher the level at which the X is seen the lower the density. 

The Spirulina Growing Manual is also available in PDF


Culture medium provides Spirulina with the nourishment it needs. It is added when increasing quantity of Spirulina and after harvesting.

Mix water and fertilizers according to quantities described above. The amount of culture medium depends on the quantity of Spirulina and should be roughly at a ratio of 1:1. For example: For 20 liters Spirulina, prepare 20 liters growing culture.

Fertilizers should be fully dissolved in the water before adding it to the Spirulina. This may take a few hours, depending on the specific fertilizers used. Agitation can speed up the process.

Culture medium can be prepared in large quantities in advance and used upon need, but should be stored in closed containers and in the shade.

The pH level of the culture medium should be 8-8.5. This can be tested with litmus paper. If pH level is lower, add Sodium Bicarbonate. A higher level is fine. 


  • After preparing a growing culture for a number of times, this stage of examining the pH level of the growing culture will not be necessary, as the color of the solution will be a sufficient indicator.


Increasing the quantity of Spirulina is done with a Spirulina culture that is mature and dense. In optimal conditions, Spirulina reaches this state within 24-48 hours. In less that optimal conditions it may take longer.

To increase the amount of Spirulina, mature and dense Spirulina is diluted with culture medium (water and fertilizers) in a ratio that is roughly 1:1, thus multiplying the quantity. For example: 100 liters culture mediums are added to 100 liters of mature and dense Spirulina. The new quantity of 200 liters will be diluted and thin, but given the proper care and approximately 48 hours it will once again be mature and dense and then ready for yet another multiplication.  

When increasing the quantity of Spirulina, the measurement of the pool or container must be adapted.

In a pool this can be done by placing a board or some other partition in the pool. This partition functions as a dam, and Spirulina is grown in the smaller area it creates. When Spirulina is mature and ready for multiplication, the partition is moved to create a larger and larger pool until it reaches its full size and Spirulina quantity. It is then ready for further increasing of quantity (another pool, for instance) or harvesting.

When growing Spirulina is a container this can be done by moving the Spirulina to a larger container.

Dividing Spirulina and adding growing culture will have lowered pH level. Due to chemical changes that result in its metabolism it will again reach its optimal level of 10-10.5.

During this period, Spirulina needs to be tended to as it was during the first stage, i.e. agitating and adding water to compensate for evaporation.

Examining pH level is done as it was done during the previous stage.

When pH level has returned to 10-10.5, it is advisable to give it a week or so to further strengthen and stabilize and it is then ready for another cycle of multiplication or for harvesting.


Harvesting during morning hours is best for both nutritional and practical reasons.


Harvesting is done in the following manner:

Hold filtration cloth over the pool or container;

Pour culture onto cloth. This can be done using a bucket or any container, but make sure it is cleaned before and after use;

The Spirulina will remain on the cloth. The culture medium will flow through the cloth and return to the pool;

The Spirulina on the cloth will at this point still have some residue of the culture medium. In order to bring the Spirulina to a pH level that is healthy for consumption (7pH), these residues need to be eliminated. To do so, press the filtering cloth (with the Spirulina in it) evenly and gently. The culture medium - which is transparent - will drain from the cloth.


When the water draining through the filtering cloth is no longer transparent but green, stop squeezing - this means that all the culture medium has been squeezed out and the Spirulina is at a healthy pH level.

The drained and pressed Spirulina should at this stage be similar in texture to paste.


  • Filtration cloth should be thoroughly rinsed with water after harvesting until there is no green residue on it and it has regained its original white color.

After harvesting, the nutrients that the Spirulina fed on must be replaced by adding culture medium to the pool or container. The amount of culture medium that needs to be added depends on the amount that was harvested, for instance: After harvesting 100 liters from the culture add 100 liters of culture medium to the pool.

Spirulina harvesting filtering cloth
Spirulina harvesting filtering cloth
Spirulina harvesting filtering cloth
Spirulina harvesting filtering cloth
Spirulina harvesting filtering cloth
Spirulina harvesting filtered algae
Spirulina harvesting filtered algae


Spirulina is at its nutritional best at this stage, freshly harvested. At this stage it is also almost odorless and tasteless, and can be mixed with and beverage or food (preferably not hot, as heating decreases some of its nutritional values).

Spirulina that is mot consumed immediately after harvest can be frozen (in sealed plastic bags or containers) and kept for 2-3 weeks. It can also be dried.


Drying Spirulina is a more efficient and long lasting option. In its dried form it can be kept for many months, as long as it stored in clean and damp free containers.

Drying is done in the following manner:

  1. Spread Spirulina on net - Using a finger (gloved), knife or spatula (cleaned before use), a plastic bag or syringe (disposable or cleaned before use) spread Spirulina on net in noodle-like stripes.

  2. A net enables drying from top and bottom. This will shorten the time needed to dry and lessen the danger of contaminators (when Spirulina is harvested it is no longer protected by the high pH level of the culture medium).

  3. It is best that this net be placed inside the greenhouse. This will further protect the Spirulina from contaminators.

  4. Approximately 2 days should be sufficient for drying.


Drying can also be done in an oven - electrical or solar.

Dry at 40°c for 16 hours or at 60°c for 4 hours (the lower the temperature the more nutritional value).

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