Phenidone/Vitamin-C Developers - One-Shot vs Re-use?

I've been using PCB reusable developer (Phenidone/Vitamin-C/Borax) for a while now and it works very well.  When I started with PC developers I used one-shot versions because that's all the data that was available to me at the time.  I liked the consistency of one-shot use but did not like the amount of chemicals that was being wasted which lead me to reusable versions such as PCB.  I found that using "normal" film is fine with PCB but lately I've been playing with Shanghai GP3 in 120 format (it's cheap and looks good to me) and what's interesting about this film is that it makes everything blue.  I'm not talking slight blue tinge here, this is like blue ink.  I doubt it makes a difference photographically but PCB is normally clear and just doesn't seem right with this strong colour.  This made me take another look at PC developers for one-shot use with the goal of minimizing waste.  After much reading of articles and forums, particularly those tidbits from Patrick Gainer, I learned that I could develop much more film with fewer chemicals and in the process I picked up some interesting information as well.  Here are a few points I put together about this:

1. The lower limit for an effective alkali in a PC developer is 0.05M/L (e.g. 5g/L sodium carbonate).  Less than that and activity drops substantially.  My own testing confirms this.
2. The ideal ratio of Ascorbic Acid to Phenidone is 40:1.  Going above this does increase activity but not by much and going below sees significant activity loss.  This is the ratio for PC-Glycol solution which we'll get to in a bit.  My testing confirms this as well.
3. Phenidone at 0.02g/L is about the lower limit for normal activity levels.  You can go as low as 0.01g/L but the developer is much slower and lower than that is very, very slow.  My testing confirmed this.
4. Phenidone can produce base fog ... it's little, but it's there.  Using 0.2g/L potassium bromide practically eliminates fog without affecting activity.  This has the added benefit of improving stand development.  My early experiments with stand development sometimes showed uneven development that was corrected with more agitation (it's no longer stand development).  Using potassium bromide gives very even development with full stand development.  Again, confirmed by my own testing.

Borrowing heavily from the work of Patrick Gainer, I propose a very economical and effective one-shot PC developer we'll call PCM (Phenidone / Vitamin-C / Metaborate) as follows:

Part A (a.k.a. PC-Glycol):
  Ascorbic Acid - 10g
  Phenidone - 0.25g
  Propylene Glycol - 100mL (warm/heat to fully dissolve ingredients)

The propylene glycol serves no photographic purpose but is a convenient way to store the ascorbic acid and phenidone in correct proportions without worry of it oxidizing.  This will last indefinitely until you add water.

Part B:
  Potassium Bromide - 0.2g (make a 10% solution as it's easier to measure)
  Sodium Metaborate 1% - 1L (6.92g borax + 1.45g sodium hydroxide in 1L water works as well)

Use 8mL part A for every 1L part B.  You can use borax (19g/L, add more time) or sodium carbonate (5g/L, less time, grain is more pronounced) but I chose metaborate as it's the middle ground giving good activity with nice grain.  Using the formula as above is an 8 minute normal developer giving box speed.  Full stand development (60 sec initial inversions only) for 90 mins gives a +2 push with highlight and contrast control.

When you break it down, developing a roll of 135 film in an 8oz/250mL tank uses the following:

  Ascorbic Acid - 0.2g
  Phenidone - 0.005g
  Potassium Bromide - 0.05g
  Borax - 1.73g
  Sodium Hydroxide - 0.36g
  Water - 250mL

It's very economical, one-shot, flexible, and consistent.  Results are virtually identical to PCB.

MM
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