Thanks for the advice Tom.
According to the "Fertilator" i will need 2.5 teaspoons in a water column of 150 gallons to get potassium redings of 10 ppm.
What i intend doing is adding this amount initially once a month and see how things pan out. If there is no sign of K deficiency on the leaves i will keep status quo. Otherwise i may add fortnightly. It will have to be a wait and see approach.
I have just bought a bag of KCl so i'm stuck with this for the time being.
If i have no readings of nitrates then i will supplement K as KNO3 instead and do without KCl
LAKA