Though sodium bicarbonate is easy to find in most food stores, it tends to come in small packets, and as you will discover, those are never enough when growing spirulina at home.
This deal is by an Amazon bestseller who is providing the Bcs in 2 or 4 bags of 3 Lb. or 6-12 Lb. in total.
They also have discounts when buying a bulk amount of 50 Lb. or more.