My understanding is that zinc anodes do not have the electrical potential to overcome the greater resistance offered by freshwater. Do what the catalog recommends, don't necessarily take what your dock neighbors suggest as gospel. There is a lot of ignorance and bad info out there. The local experts would be marine electricians or hull cleaners.So this confused me--why would they recommended zinc anodes for salt water, aluminum for brackish water, and magnesium for fresh? That seems out of order.