King Neptune, I believe your still putting your tank together, so if your trying to remove some stubborn crud, vinegar and water works pretty good as a glass cleaner. (1/2 cup vinegar to 1/2 gallon water in a clean spray bottle)
After a tank is running, and your trying to keep the outside clean (IMO, this is much more difficult than keeping th inside clean on a saltwater tank) I'm with Florida Joe. Plain water is best. I wipe it on with a clean paper towel, and remove it, streak free, with a $2 squeegee I got a the drugstore.