Neal is correct. Read about the working properties, and how exactly to do it, from Kodak.
The following Kodak publication also discusses replenishment on pages 15-17 (including XTOL).
Replenished XTOL starts as stock solution. For each roll [180 square inches] add 70ml stock solution.
I pour part of the used XTOL back into the bottle add 70ml*number of rolls stock solution then pour in the rest of the used solution until the volume is 1 liter or 1 Quart.
It doesn't need to start as stock solution you can season it with E-6 First Developer starter, or other starters, instructions in the Kodak datasheet.
It's stock times + 10% iirc according to the Kodak sheet.. generally speaking, but the Kodak sheet does list replenished times.
Originally Posted by mexipike
One practical advantage that few people reference is that a replenishment regime means that your "working" developer" is always at room temperature - if room temperature is near 20C, this means no temperature adjustment.
I use replenished HC110 which is more complex than X-Tol, but otherwise very nice.
If I had a bit more room for storage, I would transition to replenished X-Tol.
It is so convenient not having to worry about wasting developer, due to the difference between the minimum quantity of developer needed to avoid premature exhaustion vs. minimum quantity required to cover the film in the tank.
I, like Matt, used replenished HC-110b, used it for 5 or 6 years and thousands of rolls of film, 95% of it TX. What it did, it did extremely well, but it was very difficult to work with in some regards that no matter how I struggled I couldn't fix, and my work hit a point where I couldn't have those problems.
Originally Posted by MattKing
Then I tried Tmy2 in replenished xtol. Over the past 6 months I've been working with that. It took me about 50 to 75 rolls to begin to understand it - it is a BIG jump from TX and hc-110b - and a lot of that was getting over old biases and habits as far as a negative and printing, but now that I've begun to figure it out and I can't believe I've been missing it for so long. It's not that it is fully capable as far as making a great photo, almost all films and devs are, it is more that it is extremely easy to work with, from storage, to stability, to mixing, to how it responds to agitation and temp. I'm still a bit stunned at how easy it is compared to what I was doing, and quite frankly, how much better my prints are for it.
But this is all an aside, back to the OP, the replenishment process is great. Don't get caught up on the stability or the developer loosing it's action...xtol stock has a shelf life of something like 6 months doesn't it? After seasoning it's really really nice in a way that I won't bother trying to explain here since others have done that in other posts. Just give it a try.
Replenished X-tol also works well in one of the old Kodak 4x5 hard rubber tanks with a floating lid. I used this system for years, putting either Jobo or Patterson plastic reels on a pair of joined stainless steel rods. The only issue was all the development through fix had to be in the dark. The process was simple - take off the floating lids for X-tol, stop bath, fixer, and Permawash, load the reels, and develop film. It was much quicker than measuring, pouring, etc. The process worked wonderfully well and gave great negs for wet printing or scanning and no appreciable loss of film speed. Replenishing with pouring back and forth isn't as convenient, but it works.
I started my 1.6 litre replenished Xtol batch 6 years ago and it has worked absolutely consistently and predictably ever since. My replenishment rate is 90ml per "standard film". Apart from occasional filtering through a coffee filter it has never needed maintainence. All my films go through this developer; just with different times established by testing.