Potassiums role is fairly misunderstood as far as I can tell. There is alot of it in NSW, nearly in the same concentration as calcium. The amount of dosing that you will be doing isnt likely to cause a large change in potassium.
When I mixed up my KNO3 solution for dosing, I used the Greenlight stump remover, and mixed 10 tsp. into 1 quart of water. This has lasted me a year.