I don't know if this will work for you as it depends on the quality of your tap water.
Since the biggest expense of making colloidal silver is the distilled water, you can try this
Double the process time for your batch size per your process time table using distilled water. (make 40 ppm)
Use the normal amount of electrolyte (do not double it)
Add twice the amount of reducing agent (corn syrup) you would use for that batch size before starting electrolysis
Process cold or warm the water, does not have to be boiling.
When done, heat to boiling to complete reduction.
Dilute with equal part of tap water or use as 40 ppm.