About keeping the solution I'm just going by what Doremus said... question is, how much replenishment?
Originally Posted by Doremus Scudder
Also, I strongly recommend not discarding your toner, but rather replenishing it with small amounts of concentrate when the toning times get too long. The working solutions can be stored almost indefinitely; I have two gallon jugs that have been going for at least 8 years now (more likely 10+ years) and tone just fine. The toning solution needs to be filtered before use, as a black precipitate often occurs, but this is easy; a coffee filter in the funnel and you're set.
Reusing the toner instead of discarding it prevents the toxic selenium from being introduced into the environment. Even municipal water-treatment plants do not deal well with heavy metals. Plus, it is more economical and, as a desired side-effect, the solutions quickly lose the annoying ammonia smell and are more pleasant to deal with. I've been on my soapbox about this for some time here now, so a quick search on my name will turn up more info.
As mentioned, I have been doing this for years now. My fiber-base prints all test excellent for residual hypo and residual silver after two-bath fixing, toning in replenished toner, a 10-minute wash-aid treatment (HCA or equivalent) and a minimum one-hour wash.
Hope this helps,