Hi JHK;

I've been responsible for up to 24 large commercial pools (100,000+ gallons) in a season, and averaged 1/4 green pool per season out of 24. In other words, in 4 years, I had one pool out of 24 turn green 1x during a single swim season.

Does that answer your question?

Regarding the soda ash (sodium carbonate), use borax instead. But, unless you have a concrete pool, don't worry about trying to get the saturation index right, or the pH up to 7.6. Anywhere between 7.0 and 7.8 is fine.