they sell fish safe glass cleaner.....The water eventually will stain and get harder to get off, if you keep it clean it is easier. I keep a T-shirt handy and when the glass gets wet (every time) I use the moister to clean the glass tank water will suffice as lubricant, its more what you use as a "wiper" than the cleaner (lubricant). A T- shirt seems to not scratch at all as terry cloth seems to over time, Newspaper and tank water is an option as well (works for glass and aqurilic)......
As for your fish maybe GT/Syn hybrid?......