I was helping out with the mixing at the previous swap and the ESV from what I seen mixes the most quickest, although there are multiple parts. Its not complicated, just gotta follow directions.
As for the IO, I'm using the regular. My theory, and keep in mind I'm no scientist, is that the mixing process causes some of the Ca to precipitate because it might be super high concentration in 1 spot of the mixing bucket before its fully dissolved evenly which is why the Ca is lower. This might explain why my mixing bucket usually has some white residue on the bottom after I'm done. Although I could be completely wrong.