freshwater dip does nothing or least helpful to marine ich i think.
here are something u might wanna check out
u might as well check out some faq on www.wetwebmedia.com
i read on there they don't even think freshwater dip works at all.But cuz they are faqs i can't really find where it is now.
I am just wondering, since u have a nano tank, why not just remove the fish and use some strong medication such as copper? Since neon goby is so hardy i wouldn't think it will be a problem to leave it in a QT
for 8 weeks till ur nano tank clear of ich which is the best way to do it.