I would remove the galvinize from the steel before welding. Then any low hydrogen rod should be OK. If I weld over galv w/o removing it I use a E6011 rod first then a E7018 on the next layer. It also depends on what is being welded. If it is structural, you should follow the WPS. 6011 most likely would not be allowed. But I do not know of a special lohi rod for galv. You can go to http://www.lincolnelectric.com/ and search the consumables for a breakdown on the rods.