How to Start a Home Spirulina Culture (Without Guesswork)

Spirulina is a good first culture because the same alkaline chemistry that makes it grow keeps most contaminants out. You need three things: a live starter culture, a suitable vessel, and correctly prepared medium.

Start with a living starter, not dried powder — dried Spirulina is dead and will not revive. A healthy starter is deep blue-green and smells faintly earthy. Because Spirulina reproduces by fragmentation and doubles roughly once a day under good conditions, even a small starter builds up quickly. Choose a clear vessel that lets light in; wide, shallow shapes expose more culture to light than a tall narrow one. Clean thoroughly and rinse — no lab sterility needed, but no soap residue either.

Prepare the medium before adding the culture: warm, alkaline, bicarbonate-rich water — a Zarrouk-type medium dominated by sodium bicarbonate (on the order of 16 g/L) plus nitrate, phosphate, potassium, iron, and trace minerals — at pH 9.5–10.5, using non-chlorinated water. Inoculate relatively dilute so the young culture is not shaded, then give it ~30–35°C, bright but not scorching light (~100–250 µmol/m²/s, 12–16 h/day), and gentle daily mixing. Over one to two weeks it should deepen from pale to rich green. Resist harvesting early; a dense culture is far easier to maintain than a thin one.