Thank you Jay. I’m going to try to take pictures.Sorry - your copper treatment with the Hanna test should be spot on.
Letting a device dry for 12 hours with no other disinfection is not likely to be 100% effective - water could still be hiding under the knob, the suction cup brackets, etc. Soaking in FW and then drying for 24 hours is a better bet. Still, it isn't like the ich tomonts seek out places to hide, it is more or less random.
As you, white spots don't always mean ich. I've not heard of a copper resistant strain of Cryptocaryon in any studies, just rumors. Certainly bacteria develop resistance to antibiotics, but it takes multiple treatments, with the same antibiotic to create resistant strains. Copper is a toxin and less likely to create resistance. I do know that people have gone with higher doses with copper power in order to knock ich out, but that may be a function of the product, not the disease.
Jay