Stone:

X-Tol easily lasts 6 months once mixed, and it is easy to mix. Past that, it is a bit iffy, but it is cheap, so if you need to toss it after 6 months, you are probably wasting between 3 and 7 dollars.

When you mix it up first time, you divide the 5 litres into a bottle used for working solution and bottle(s) for replenishment. I'm currently using a 1.25 litre bottle for my working solution.

You only need to replenish it a minimum of once a week, and you do that by just dumping 70 ml from your working solution and adding 70 ml from your replenishing solution - which comes from the same initial 5 litre batch. You only need to do this during any week when you don't develop film.

If you actually develop film during that week, you replenish after each development @ 70 ml per 120 roll or equivalent (120 = 135-36 = four 4x5 sheets). You dump the appropriate amount of replenishing solution into your bottle while the film is developing, and than pour the developer back into the bottle, with the excess being discarded.

Your first batch will give you about fifty 120 rolls (or fifty 135-36 rolls, or 200 4x5 sheets). With subsequent batches, you continue to use the same bottle of working solution, while the newly mixed batch can be conveniently split between five one litre bottles.