CS>OT - zappers

[PT Ferrance]

I just got a 3 frequency zapper (15Hz, 2.5KHz and 30KHz) and there is no 
printed 
material that came with it on choosing the best frequency.  All my books are in 
storage.  Can someone help me out?  I zap 7 minutes and rest 20 minutes for 3 
cycles, I've read but I don't know if I do each cycle with the same frequency 
or 
if I go from one frequency to the next.  Does anyone know how to proceed?
Thanks.
Merry Christmas.
PT