Glass tops you can always rinse with a hose, so look for a product called CLR. It's designed for removing lime deposits.
If that doesn't work, the most serious thing around for cleaning glass tanks & such is Sno-Bowl toilet bowl cleaner. Read this warning twice;
It is concentrated hydrochloric acid, it will eat away your skin, the fumes will cause lung damage.
Get a pair of heavy duty acid resistant gloves, a long sleeved heavy shirt or jacket, and wear glasses or safety goggles. Your best bet is using this outside where there is plenty of ventilation, and you will be rinsing whatever you are cleaning with a hose. If you are using this on a tank be very careful around the seams unless you plan on doing a reseal. If you get any on your skin rinse immediately with lots of water.
I, as well as other folks I know have used both of these products on tanks. They are old school tricks, nobody with half a dozen used tanks is going to be using a toothbrush & baking soda for all eternity. I plan on starting with CLR on five used 40 breeders sometime in the next week or two, if it doesn't cut it out comes the Sno-Bowl. I'll try to remember some pics, I just picked up some wood for the racks this evening.