How to Farm Spirulina

Spirulina is the most forgiving alga you can grow, and the only one we sell that you can harvest with a net. It is also the one people eat. If you want to grow algae and actually hold the product in your hand at the end, this is where to start.

Why spirulina is the easy one

Two things make spirulina forgiving in a way no other strain is.

• It lives at pH 10. That is alkaline enough that almost nothing else can survive there. Your culture stays clean with no sterile technique, no autoclave, and no filtration. Contamination, which is the thing that defeats most beginners, mostly just does not happen.
• It is big. Spirulina grows as trichomes, coiled filaments 20 to 1,000 micrometres long. The tightest mesh you can practically pour a culture through is about 30 micrometres, so spirulina catches in a screen. Every other strain we sell is smaller than the mesh and goes straight through, which is why harvesting them needs a centrifuge.

Your operating numbers

Spirulina cannot be grown in plain fresh water. The alkaline, heavily buffered chemistry is not optional, it is the whole reason the system works.

Setting up

1. Make the media. Dissolve the alkali salts in chlorine free water at 15 g/L. Add nutrients at 1 mL per litre.
2. If the water turns white, that is carbonate precipitating out. Stand it 24 hours undisturbed, pour the clear water off the top, discard the sludge. Nothing is wrong.
3. Fill the vessel part way. Enough to cover the bottom and let it mix, about 6 litres in a 5 gallon setup. You grow into the volume, you do not start full.
4. Add an air stone and bubble gently. You want the culture to roll over, not to froth. Hard bubbling shears the trichomes.
5. Add your inoculum. Never more dilute than one part culture to four parts media.
6. Dim light for two days, then move to full light on a 12 hour timer.
7. Build volume by adding 10 to 20 percent more media per day until you reach the volume you want.

Where to grow it

In a laboratory

Erlenmeyer flasks and culture tubes. Easy to keep clean, easy to swirl, easy to run many at once.

Inside a home or classroom

A plain 10 gallon glass aquarium is the workhorse. Light gets in from every side, and it costs almost nothing. An air stone and an LED shop light finish the setup.

Outside

Tanks, troughs, or a lined raceway pond. Outdoors, light stops being your limit and temperature becomes it. A large, dense culture handles direct sun well because it shades itself. A small or thin one does not, and will cook.

Harvesting

1. Check it is ready. Density 10 to 15 g/L, deep blue green, and the Secchi reading has been stable for a couple of days.
2. Pour it slowly through the harvesting screen. Slowly. Let it drain rather than forcing it.
3. Keep the media that runs through. It is still good media. It goes back in the tank.
4. Rinse the algae on the screen with cold tap water. This matters if you intend to eat it, because the growing media is alkaline and you do not want it on the product.
5. Stop when it behaves like a paste. That is your biomass, and the harvest is done.
6. Blow down 10 to 20 percent of the recycled media and top back up with fresh. This keeps salts and waste products from building up over many cycles.
7. Replenish nutrients at 1 mL for every 1 litre of culture you took out.

Done this way the system runs indefinitely. You never start over, you just keep taking product off the top and feeding it back.

Common questions

Can I use Miracle-Gro?

We do not recommend it. Garden fertilizers are formulated for soil and land plants, and the nitrogen form, the phosphate load and the missing trace metals and vitamins are all wrong for spirulina. You will usually get a weak culture that is more prone to crashing. The nutrient cost is not where your money goes in this hobby.

Why is my spirulina clumping at the bottom?

Usually nutrient starvation, the end of a batch run, or both. Stressed cells make sticky polysaccharides and stick together, and clumps sink. Add fresh media first and see if it recovers. Also check that the mixing is actually turning the whole volume over.

Is it safe to eat?

Spirulina you grow yourself is food you are producing, and it deserves the care food production deserves. Rinse the harvest, keep the culture visibly clean, know what is in your water, and do not eat a culture that smells wrong or has an unexplained colour in it. If you are selling it, that is a regulated activity and the rules are not ours to give you.

Everything else

Setup, light, media, measuring growth, and what to do when something goes wrong are all covered in full on our main culturing guide.

How to Culture Algae

• Spirulina Farming Kit instructions
• Mix your own alkali media
• Lighting
• Temperature
• Growing vessels
• Harvesting
• Spirulina density chart
• Algae culture and pH