Maris said:
My developer is about five years ripe. The one litre working strength bottle of X-tol is replenished at a rate of 90ml of X-tol per film developed. <<<
Actually, of course, with the 90ml/film replenishment rate there would scarcely be an atom of the original mix still in the stock bottle. You could say the developer is "seasoned" rather than "ripe".
I ran a tankline for a year and a half or so with XTOL and did the same thing, but the rate was 80ml for me. after I got seasoned, it ran very well, albeit with a slight loss in speed, as expected. I estimated that I turned it over (volume) about three months or so, and I would filter out the bromide sludge if it got too heavy on the bottom of the tank. I was testing it to see if we could change over from TMAX RS to that, but in the end I stuck with RS. XTOL I think you probably run indefinitely in the tank replenished though...there may be some specific gravity problems and the like eventually, but it seemed incredibly robust as a working developer.
I run a TMAX RS deeptank line where I work and we go for about 2-3 mos, and then dump & remix. like XTOL you adjust up or down, and use the same soln. to replenish, so it's almost impossible to screw it up. I used to run control strips as well, but using the same chemistry to replenish makes control so much easier, that you don't really have to do that anymore....
I used to do mini-versions of these tanklines at home using one-gallon tanks, but I quit about a year ago. I wasn't running enough to be economical--I had to replenish at higher rates, and it became more of a hassle really, so I went back to using one-shot HC110. Although I use AB55 as well, and reuse that. I still process film in a tankline though--even as one shot because I can't quite ever see myself going back to a daylight tank....