Since you don't use shore power, do you have any other shore connections like cable TV, data cable etc.?
If there are no shore power connections the electrolysis
is being created locally on your boat. Are you in fresh water
? Magnesium is a high voltage zinc for use in fresh water
. In salt water
you should use normal zinc zincs. Magnesium anodes in salt water
are just self destructing "over protecting" the boat.
Make sure all the underwater items are connected to the same place, typically the 12 volt negative. Check that the exposed underwater metal on each item is connected to the negative and if it is not, then bond them together with a coppoer wire. The wire carries nearly zero current
so it only needs to be heavy enough to survive in the marine environment
Once you get all underwater metal connected together any zinc loss is due to different metals in the water and you will have to live with it.
The Hoda 2000 and its strange grounding "should" have nothing to do with your electrolysis