[*]Minimum tank life of 2 months at tropical warmth;
[*]Low toxicity - probably ascorbic based;
[*]Neutral tone (not warm tone); and
[*]High volume without replenishment?
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I lived in the tropics for six years and was frustrated for three of those six. Then I discovered divided developers and lived happily ever after.
Any developer can be divided; just separate the alkaline activator from the developing agents. For a paper developer such as Dektol, for example, all the ingredients except the carbonate go into Bath A. The carbonate goes by itself into Bath B. About 20-30 seconds in Bath A, followed by about a minute in Bath B with no rinse in between will do it for you. Time is not critical, since development stops in Bath B when all the developing agents absorbed in Bath A are exhausted. It's only necessary to leave it in long enough to go to completion. It happens fast.
Other benefits: no need to control temperature. The whole time/temperature variable is eliminated. My darkroom temp in Malaysia, even with a window air conditioner was 82F, and ambient water temp was often higher.
Currently, I favor a variant of E-72 (see my article in chem recipes section) which is an ascorbic acid developer, and it can be divided easily. I no longer divide it because I'm not in the tropics any longer, but it will work just fine as a divided developer. I mix it as a concentrate (3X strength) but without the alkaline activator. When using, I dilute it 1:9 with water, then simply throw into the tray 2 Tablespoons of carbonate/liter of developer. For dividing, just put the carbonate in a separate tray.
Formula for concentrate:
Phenidone .5g
Sodium Sulfite 45 g
Ascorbic Acid (Vitamin C crystals) 19g
Edwal liquid Orthazite (benzotriazole) 10ml or Potassium Bromide 2 g
If you want to, you can eliminate the sulfite and use 6 g of Hydroquinone, turning it into a PQ developer; this might make it work better as a divided developer.
You won't need to store the concentrate in a refrigerator. It will eventually oxidize over time, but will keep fresh and active for many months. I'm 10 months into my current batch, and it's still going strong.
Larry