Spirulina

Brief summary of spirulina

6/27/20262 min read

How to Grow Spirulina at Home
A beginner-friendly guide to cultivating the most nutritious microalgae on Earth.

What You’ll Need

A clear container (a 2-liter soda bottle or a glass jar works perfectly)
Spirulina starter culture (you can revive dried spirulina powder from a health-food store)
Zarrouk medium (a mix of baking soda, salts, and a tiny bit of fertilizer – recipe below)
A light source (a desk lamp with a bright white LED bulb, or direct sunlight)
An air pump with a small air stone (like the ones used in aquariums) to keep the water gently moving
A thermometer and pH strips or a simple pH sensor (spirulina likes it warm and alkaline)

Step-by-Step Instructions

1. Prepare the growth medium
Zarrouk medium provides everything spirulina needs. For a 2-liter bottle, mix the following in clean water:

16 grams of baking soda (sodium bicarbonate)
2 grams of sea salt or non-iodized table salt
0.5 grams of potassium nitrate (available as stump remover or in hydroponic shops)
0.1 gram of a complete plant fertilizer (like Miracle-Gro, just a pinch)
Optional: a drop of iron supplement (liquid iron for plants)

Dissolve everything well. The water will look clear with a slight blue-green tint.

2. Add the spirulina starter
If you have a live culture, pour in about a cup of it. If you’re using dried spirulina powder, sprinkle a teaspoon into the bottle and stir. Place the culture under light and wait a few days – the live cells will slowly wake up and start multiplying.

3. Set up light and aeration
Position your lamp so that it shines directly on the bottle. A light cycle of 12–16 hours on, 8–12 hours off works well. Plug in the air pump and place the air stone at the bottom of the bottle to create tiny bubbles that keep the algae suspended and supplied with carbon dioxide.

4. Keep conditions stable
Spirulina thrives at:

Temperature: 25–35°C (77–95°F) – room temperature is usually fine, but a warmer spot speeds growth.
pH: 9.0–10.5. If the pH drops below 8.5, add a tiny pinch of baking soda.
Light: Bright but not scorching. If the water gets too hot, move the lamp a little farther away.

The culture will turn a darker, richer green every day. That’s the sign of healthy growth.

Common Problems and Easy Fixes

Yellow or pale green culture: Not enough nutrients or light. Add a small amount of fertilizer and increase light duration.
Clumpy or sinking algae: Insufficient mixing. Check that the air stone is bubbling strongly enough.
Bad smell (like rotten eggs): The culture has been overrun by bacteria. This usually happens if the pH is too low. Keep pH above 9 and start fresh if needed.
Foam on the surface: Normal – it’s just proteins. Don’t worry.

Harvesting and Using Spirulina
After 7–10 days, your culture will be dark green and ready to harvest. Pour some of the liquid through a fine cloth or a coffee filter. Squeeze out the excess water and you’ll have a thick, green paste. Rinse it briefly with fresh water, then eat it right away or refrigerate. You can also spread it thinly on a tray and dry it in the sun or a very low oven to make your own spirulina powder.

Start with small harvests and always leave enough culture behind to regrow. With a little care, your spirulina farm will keep producing for months.

Happy growing! If you want a system that automatically monitors pH, light, and temperature and even adjusts itself using AI, check out our Global Algae Optimization Network