Actually RA4 blix lasts at least a couple months once mixed, but it does deteriorate.
Originally Posted by nworth
My solution is to mix the bleach and the fix each with water so that a 1+1 mixture of those two intermediate solutions will result in blix replenisher at the right concentration. So when printing you don't need to worry about dilution ratios but you don't have degradation on the shelf from the bleach eating the fixer. In other words, don't make up 10L of blix, mix the bleach into 5L and the fixer into 5L and store them separately.
When replenishing, you just use half as much of each; e.g. if you wanted to replenish blix by 50mL then you would use 25mL of each intermediate. A split replenisher, as it were; the net result is the same quantity of active ingredient going into your working solution.
You can't (with the Kodak RA RT at least) run the bleach and fix baths separately because there's a buffering agent in the fixer part that is required for the bleach to work to completion. If you run them separately then you will have silver retention, therefore poor saturation and high contrast.