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An old dataguide I have recommends replenishing single bath D23 with DK-25R.
Water. (125/52) 24oz(750cc)
Kodak Elon Developing Agent. 145 grains (10 grams)
Kodak Sodium Sulfite, dessicated. 3 oz and 145 grains (100 grams)
Kodalk. 290 grains (20 grams)
Add cold water to make. 32 oz (1 liter)
For d23, replenish with 3/4 ounce for each roll processed or 80 square inches (520 square cm) of film. After ed rolls you might have some loss of shadow so keep an eye on it.
I do just that, and my last batch of D-23 was finally laid to rest after 3-1/2 years of use. I keep it in a brown glass bottle, filled to the brim, with no air space. My method for replenishing is to add the replenisher to the bottle, and then top with the used developer. If I think that I will come up short, usually due to spillage, then I will mix a pinch (like 150mL) of fresh D-23, add it to the bottle, add the replenisher, and top with the used solution. The excess is then dumped.
I don't have my Photo Lab Index in front of me, but AFAIR, Kodak recommends no more than about 25 rolls per quart/litre be processed, with replenishment. The capacity, without replenishment, is 4 rolls per quart/litre. So, in a 4-litre bottle (and my 1-gallon bottle actually holds 4.06-litres), you can process 84 rolls, with replenishment, and another 16 rolls, without replenishment. You would need to have mixed 84 x 3/4-ounces of replenisher, or just shy of two quarts.
The rough rule of thumb for replenished, but non-monitored developers, is when the volume of replenisher added equals the original volume of developer, you can then use the developer to the limit of its non-replenished capacity, and dump it. I used to do that many years ago with Acufine; mix a quart of deveoper and replenisher, ad 3/4-ounce after each roll, and when the replenisher had all been added, you could develop four more rolls, before sewering the developer.