How much sodium alginate to make a reverse sphere?

Sodium alginate is the primary gelling agent used when making spheres and the wrong amount in your water bath does play a big factor. Too little of this may prevent you from setting your spheres, and too much may result in too thick a membrane. Like all other molecular cuisine ingredients, the best way to use sodium alginate is according to the suggested ratio.

The amount will depend on the amount of calcium lactate used in the base. If you put in 1% to 3% calcium lactate in your base, then you will need 0.4% to 0.5% of sodium alginate in water bath to successfully set spheres that have the right membrane thickness and consistency as well. I hope this works for you, good luck!