It is not the customers job to tests for CFUs, it is the job of the seller to prove that it is actually working. People do not just buy zappers to feel better or to get some hokey reading like the synchrometer.
They want and are entitled to proof that it does what you claim.
As stated before, if you can not show that it is thorough in killing the microbes in a jar of pond water, how can the expect it to be able to work in a more difficult situation.
And you say that your accuracy is "one millionth", how is that possible with only 250,000 frequencies? The numbers do not match what you claim.