In Europe, Calgon powder now contains zeolite, no mention of phosphate:
To remove hardness from water I add 1 teaspoon of this to a gallon or 5 L tapwater,stir well,allow the resulting suspension (zeolite?) to settle overnight.The mostly clear water now with no calcium hardess is decanted to a container.
To confirm hardess removed I added potassium carbonate solution,it gave no cloudy calcium carbonate precipitate whereas untreated tap water does give cloudiness.
IMO this type of Calgon powder should not be used in old formulas calling for Calgon,it would likely form a cloudy suspension.
Zeolites can exchange ions in the reverse direction, and thus release the Calcium when the developer is mixed with the zeolite. In a Sodium Carbonate developer this equillibrium could then result in formation of Calcium Carbonate during keeping.
In addition, the solid zeolite that forms can be abrasive to film or get trapped in the wet swollen emulsion.