Sometime this week I learned a very important piece of information for using fiber reactive dyes, that I hadn't known about before ~ and now I know why trying to use the dye recipes I've used for years with acid dyes weren't working with the fiber reactives: the primaries need to be mixed in different proportions for fiber reactives. In other words, red is three times as strong as yellow, whereas blue is twice as strong. This applies to any red (including fuchsia), any yellow and any blue (including turquoise). If you were "raised" on fiber reactives, you undoubtedly already know this. But acid dyes are of equal strength, and that's where I started dyeing.
So, if I want to recreate an acid dye formula with fiber reactive dyes, and the acid recipe calls for 6 parts yellow, 1 part blue, 1 part red ~ the fiber reactive formula is 18 parts yellow, 2 parts blue, 1 part red. Every yellow part gets multiplied by 3, every blue part by 2, every red part by 1.
I did this very thing with the dark magenta I used for shibori yesterday, and the resulting fiber reactive color perfectly matched the acid dye swatch. Now I know how to make this work for me, and I have a huge color book of formulas I can recreate.