What do microalgae need to grow?

Four inputs: light (not too little, not too much), a nutrient medium matched to the species, a workable temperature, and mixing or agitation that keeps cells in the light and gas exchange happening. Everything else is refinement.

How long does a culture take to grow?

It depends on the species and conditions. Under good conditions many cultured species double daily or faster in early growth phase, then slow as density rises. Timelines differ by species and setup — track your own doubling times rather than trusting generic numbers.

Why did my culture turn pale or yellow?

Common causes: nutrient exhaustion (the culture ate its medium), light stress or photoinhibition, temperature outside the comfortable range, or contamination. Pale growth after a dense phase is often simple hunger — subculture into fresh medium.

How to Grow a Microalgae Culture

Growing microalgae looks intimidating and is mostly bookkeeping. Every culture, from a test tube to a 1,000-litre tank, needs the same five things managed: light, nutrients, temperature, mixing and cleanliness. Get those boring five right and the biology mostly takes care of itself.

The five inputs

Vessels. Start small: flasks, bottles or small columns. Transparency matters more than shape — light is the limiting input in most small cultures. Keep vessel size consistent within a batch so comparisons mean something.
Light. Microalgae photosynthesise, but more light stops helping and starts hurting (photoinhibition). Bright indirect light or moderate LED photoperiods suit most cultured species; intense direct sun can cook small volumes. Each species guide we publish notes its own comfort zone.
Nutrients. Standard media exist so you do not have to formulate chemistry: Guillard's f/2 for marine species, and comparable formulations for freshwater species. Nutrients run out — a dense culture strips its medium in days, so plan to subculture or dose.
Temperature. Most cultured microalgae are comfortable at room temperature or slightly below; tropical and temperate species differ. Consistency matters more than the exact number.
Mixing. Shaking, aeration or gentle stirring keeps cells in the light, prevents settling and strips oxygen buildup. A culture that sits still stratifies and sulks.

Monitoring without a laboratory

Three cheap observations carry most of the information. Colour and density by eye: a healthy culture deepens in colour daily. Settling: cells that sink out or clump are telling you something. Smell: fresh cultures smell green and vegetal; sour or putrid smells precede visible crashes. Optical density (OD) measurements make it quantitative when you are ready — Algaephyte exists largely because we wanted that loop closed automatically.

The rhythm

Cultures are perishable machinery. They grow, peak, then decline as nutrients exhaust and metabolites accumulate. The craft is in the rhythm: subculture or harvest near peak, keep back-up cultures at smaller volume, and never let your only culture of a strain be a five-litre bottle on its last legs. Our guides to starting cultures, preventing contamination and scaling up cover the transitions.

One honest caveat: parameters published anywhere — including here — are generalisations. Strains differ, water differs, seasons differ. The species pages give each organism's general tendencies; your own logbook gives the truth.