Some years back, I read of someone having longer storage life with their Xtol stock being mixed to a higher concentration. I mix my Xtol into 1 gallon of distilled water in a glass thumb jug, gently rolling the jug back and forth to avoid aeration. I then decant to small brown bottles, topped up as much as possible. I have a spreadsheet-generated grid posted in my darkroom (attached) with the various stock amounts to convert to standard (as if mixed at 5L) 1:0, 1:1, 1:2 and 1:3 for the tank sizes that I use. I've had great luck with this over the years and find it much easier than wrestling with methods to accomplish 5L batches. I like Xtol but it's not my main go-to soup and the extended shelf life for my usage patterns works well for me (I've never suffered a fail to this point).