I used it from the stock solution for several years when I was shooting a lot of 35mm. I would mix the stock and put it into pint brown bottles. By time I got to the bottom of the second bottle, it was getting pretty brown, but it lost none of its activity. At that point, I often would mix a new batch of stock and add the old brown remains of the last batch in just to temper the new stock a little. Whether or not this made any difference, I didn't notice, but it was a nice little ritual.

Peter Gomena