concentrate developer life - pushing the air out of the bottle

Howdy.
I have been using Ilford lc29 one shot. When ever I mix up a batch, I always ensure that I refill the concentrate bottle with some glass beads to bring the level up and tightly recap. According to the spec sheets, lc29 should keep for 36 months in unopened bottles and 6 months in half full opened bottles.

Considering that I am pushing the air out and considering that the bottle isn't perfectly factory sealed, what would be a fair lifespan for a bottle such as this? Is there an easy way to test the developer?

I am thinking of trying DD-x next. what considerations would I need for long storage life of this developer (considering that I shoot on average 2 rolls a month)

Cheers

I would suggest that you should get 12 months or more doing that.

An alternate method is to decant from the concentrate bottle into a series of much smaller bottles. Here in Melbourne, I got some from a place which sells oils, etc in sizes of about 10ml, 20ml, 50ml and 100ml.

As to the LC-29, I too have some on the go. I use it as though it were HC-110, becuase as far as I can tell, this is just like ilford's ID-11 equal to d-76.

I draw 16mL of lc29 into a syringe and dilute it into 500mL of distilled water for a working solution for a 120 roll. I try not to develop a 120 roll with less than 500mL of working strength developer.

No need to dilute it per the instructions on the bottle. The concentrate on its own keeps almost forever. I pour it off into 'smallish' 220mL empty yeast bottles. Where I am they are wide mouth amber galss, with a metal lid with a good rubber gasket. The wide mouth makes it easy to get the syringe into the bottle.

I'm with Kevin on the small bottles source. I ordered a case of 12 (or amybe it was24?) 125mL amber glass with an order of essential oils for another hobby, soap making, and they were priced most reasonably there.