I have a Red Sea K test kit if you'd like to bring over some water. I'm close to you in Murray.
Contact me at 808-345-1049
You make think I'm crazy but FYI, in ~20 years as a coral farmer, I've never worried about K specifically and to my knowledge the only nutrition issues I ever had with coral came because I was not ensuring proper levels of the following, in this order: 1st) Alk, 2nd) Ca, 3rd) Mg, 4th) PO4, 5th) I and maybe Fe. Potassium never came up.
Of course I have always used Kent Coral-Vite and Kent Reef Essentials as supplements on alternate weeks, adding about 5 mL weekly in my recent 300 gal system. I just looked it up. Kent has three forms of Potassium listed in these two supplements. 
I'd be curious to hear what testing results you come up with?
I'm also curious if there is some issue with your tank that you're wondering if it is a K deficiency?
Aloha,
Mark 