DIY Turbidity Standards?

I am trying to help my high school chemistry class make their own turbidity standards to calibrate the arduino turbidimeters they are making. Last year we tried calcium carbonate as it makes a cloudy solution but I don’t think that the concentrations were very accurate since there was so much precipitate sitting on the bottom. It was recommended to me to use milk, but the idea of their standards being perishable is non ideal (and I hate to think of what would happen if a kid spilled milk all over their circuit board!) Does anyone know of any relatively safe, relatively available compounds that would produce a consistently cloudy solution for turbidity standards?


