Six Culture Signals: What a Reactor Senses

A photobioreactor is a black box unless you can read the culture’s vital signs. Algaephyte samples six continuously, and each maps to a distinct piece of biology.

pH is the fastest-moving and most informative. Photosynthesis consumes dissolved CO2 and bicarbonate, driving pH upward over the day — a rising pH signals active carbon fixation, while a climb past ~11 signals carbon starvation and an unexpected drop can flag contamination. Temperature sets metabolic rate: Arthrospira grows well from about 30–37°C, fastest for many strains near 35°C. Light is energy, but more is not better — roughly 100–250 µmol/m²/s at the surface is productive; too much causes photoinhibition.

Optical density (via turbidity) reads biomass directly and drives harvest timing. Dissolved oxygen is a stress gauge: in a dense, bright vessel O2 can supersaturate far above air equilibrium, promoting photorespiration and oxidative stress. TDS tracks the ionic strength of the medium — a proxy for nutrient and salt concentration. No single sensor is decisive; their power is combinatorial. Rising pH with rising DO and rising OD is a thriving culture; falling OD with a pH swing is trouble. Algaephyte reasons over all six at once.