As ianho has mentioned, leafzone isn't the best trace nutrient product on the market although it does contain some potassium (a macro nutrient). I'd go with Tropica Plant Nutrition.
However, deciding on what fert to get depends on your tank set up and what the plants are demanding. For example, Low tech set ups with low lighting would probably be ok with Leafzone because their demand for macro nutrients is low enough that the fish will probably supply enough. However a medium to high tech tank with more light would need a fertiliser containing micro and macro nutrients (nitrogen, phosphorus and potassium), more than what the fish can provide.
Generally it's better to dose daily instead of weekly to ensure that the plants do not run out of nutrients at any point. Simply divide the weekly dosage by 7.