Wearing gloves, apply a commercial acid-based bowl cleaner to the toilet ring and clean using a toilet bowl brush or wand. If the bowl cleaner doesn't work, try using a green, nylon-backed scrub sponge along with the acid. If the ring is old, use a pumice stone.
If you've ever had toilet bowl rings and stains, you know that they seem next to impossible to remove. Toilet bowl rings are the result of hard water and minera.
Chemical free trick to clean that nasty toilet bowl ring.. The lemon Koolaid works in the dishwasher too for removing the soap scum build up from the insides.