Hello: It seems you have fairly non-conductive water, which favors powered anodes. In the interest of science, if you have three separate systems, you could convert one tank to sacrificial magnesium rods. In your other post, you said the tanks are 199,000 BTUs, so they likely have multiple flues. This means more surface to protect. Switching to non-powered anodes might be a question for the manufacturer as it could affect warranty.
ps. I’ve not heard that bit about powered anodes not working well in tanks with lots of flow, or in bigger tanks. Do you remember the source?