During my Google search I think I read that the biological grade and EC grade (I think that's what it was called) require refrigeration. Think I'll just stick with the 2.6% for now. Who knows ... I may end up going the pressurized co2 route by this time next year. LOL
I saw that the 28 has surfactants but also saw a lot of people that are using it seemingly without problems.?? But rather than take chances just figured I'd use the 15. It's still a huge savings over Excel.
And definitely will NOT use the activator.