Newbie Zapper Frequency Confusion

Hi all,
I'm considering buying a Zapper from ZapperGuy on eBay. I am a bit confused though about these different frequencies. In Hulda Clark 's book, she says:

"Any positively offset frequency kills all bacteria, viruses and parasites simultaneously given sufficient voltage (5 to 10 volts), duration (seven minutes), and frequency (anything from 10 Hz to 500,000 Hz)."

I have trouble understanding why for example, ZapperGuy has Zappers available at 15Hz, and another that has these three frequencies: 30KHz, 2.5KHz and 15Hz

Can someone clarify what a person should purchase in order to effectively kill the parasites in our bodies? Tweet