On Jan 11, 2:39 am, "Pino" > wrote:
> How does one calculate how to add 20-40ppm of SO2?

Guy's answer gives you the exact amount. If you don't have a precision
scale, a reasonable compromise is: 1/4 teaspoon of potassium meta gives
about 50ppm of free SO2 for 5 US gals, so dilute this in a known amount
of water - say 20-25 ml - and then calculate how much of the solution
you need for your volume.

Ex., to get 20ppm for 6 US gals: the whole amount of 20ml would give
(50ppm x 5 gals) / 6 glas ~ 42 ppm for the 6 gals, so to get 20ppm, use
(20ml x 20) / 42 ~ 10ml of the solution.

This is not as precise but good enough as long as the 1/4 tsp
measurement is reasonably correct - Iverson recommends getting the
spoon form a pharmacy instead of using the usual kitchen tool.

Pp