What water quality and temperature does spirulina need to grow well?

Spirulina is an alkaline-loving microalga, so it grows in water kept clearly alkaline (a high pH maintained with the right nutrient or bicarbonate mix), in warm temperatures with strong sunlight, in a shallow pond or tank that is stirred regularly so the culture stays suspended and lit. Clean source water free of contamination is essential. Batches typically crash from contamination by other algae or organisms, pH or temperature drifting out of range, water that is too cold or too hot, poor stirring leaving stagnant zones, and dirty handling. Cooler weather slows it down. Because it is sensitive, you need to monitor pH, temperature and culture colour and act early. Get the exact pH range, nutrient recipe and temperature targets, and a water test, from a qualified trainer, a fisheries or biotech institute, or your KVK before you start, and trial small.