I wouldn’t suggest using any kind of chemical glass cleaner, for the simple reason that it is indeed toxic. Water/vinegar should be fine, but I personally just use water, and some soap if I need it. I am also using spring water, so that might explain some of it.
If your hard water is the only option, you might want to buy some gallon jugs of water from the store. The cheapest kind should work fine. Just wash your tank as it would sit, so the water isn’t wasted. After washing it with plenty of water and a wet cloth, I would dry it with a large, lint-free cloth. After that, I usually use a microfiber cloth to buff the glass, but it usually doesn’t need it.
then again, if you can find a nontoxic cleaner, that should be safe. But I would stick to soap and water if you can