What are you using for substrate? I remember reading the dosing for Brighty K is 1mL per 20 litres although I've never read the label/instructions, FYI.
Tom Barr did a scientific analysis of the ADA fert line, and without going into details, Brighty K didn't have a very large concentration of potassium at all. This is because ADA relies on their Aquasoil as the main nutrient source for your tanks.
If you were to use the ADA liquid ferts with the EI method (my preferred routine) you would waste a lot of money. My advise would be to use up the Brighty K and the buy dry ferts and using the calculator linked above, create your own liquid version.
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