HELP: Ilford DD-X question....oxidization/replenishment?

I've been developing HP5+ (135 & 120) in DD-X and getting excellent results. Two weeks ago, I developed two rolls of 35mm ( 2x 36 exp.on two reels, Patterson "system 4" tank) and it came out as expected....I saved the solution in an airtight/light-tight bottle, but only 1/2 full...One week later I developed one roll of HP5+ in the saved solution and the negs came out a bit thin....admittedly, this could indicate underexposure, but that roll was from a Mamiya 645 with the AE Prism shot as metered...subsequent rolls shot as metered came out bang on.

here is my question(s): Ilford states DD-X may be reused with a "slight loss in quality"...does this ONLY apply to the same day it is mixed? How quickly does this developer oxidize when there is air in the bottle (I don't own any 500ml Amber glass bottles to remove all possible air)???

BIG QUESTION: I have last weeks solution that developed one roll of 120....can I make another 1+4 solution and add it to this older solution to "freshen it up"? I know that some developers have dedicated replenishers, but DD-X does not and I don't have access to another developer until at least a few weeks. Would it be better to just add 20-25ml of developer to the week-old stock solution to increase its potency? (That seems like a crap shoot, since I have no way of knowing how much/fast oxidization has affected the solution!)

those of you with lots of experience, please chime in!

It is a well known fact that stock solutions of developer created by diluting a concentrate with water do not keep well and should be used within a few hours. If you expect more than a few hours to elapse before developing your next roll, it is always best to mix a fresh batch. Don't risk losing important negatives by trying to save a few pennies; it is, simply put, not worth it!

I might add that when a developer is used as Fred states that it is recommended that the development time be increased by 10 to 20%.

Fred Aspen said:

It is a well known fact that stock solutions of developer created by diluting a concentrate with water do not keep well and should be used within a few hours. If you expect more than a few hours to elapse before developing your next roll, it is always best to mix a fresh batch. Don't risk losing important negatives by trying to save a few pennies; it is, simply put, not worth it!

Click to expand...

Fred, I'll assume that was pedagogy and not condescension. unfortunately it doesn't teach me anything at all. I would've hoped that the tenor of my post indicated that I know "best practice", and simply had a technical question about a new (to me) developer. Thank you for your reply, nonetheless.

the poster below you gave 20% additional development time....that was helpful, as I would've started with 50%. Thank you, Gerald.

Hi Jimmy, I read that and then re-read it about 3 more times. I think Fred just meant that to back up what he was going to say next. As in, "my source for the info I'm going to share with you is ..." I agree sometimes things don't quite come out how we intend them (or how we would speak them) on the Internet.
This is an interesting read for me because I'm just getting back into building up a darkroom after a several year hiatus, and I had always used my developers as "one shot" with some dilution - D76 1:1, Xtol 1:1 or 1:2, so that I wouldn't have something like this happen. Mostly because I wasn't sure exactly how to avoid this sort of thing - so I just never chanced it. But nice to see there is a solution for you in increasing the development times!

See pages 9 and 10 on Ilford's DD-X data sheet for information about to adjust development times when reusing stock solution. Also note this text from page 10, "ILFOTEC DD-X, ILFOTEC LC29 and ILFOSOL S working strength solutions should not be kept for more than 24 hours. Make up fresh developer each time it is needed and discard it after the processing session."