Iron in the water supply, oxidising as it sits in the bowl. Bleach makes it worse by fixing the stain; an acidic cleaner is what removes it. If it returns within days, the answer is water treatment, not cleaning harder.
Why bleach is the wrong bottle
This is the useful part and almost nobody knows it. Iron staining is already oxidised iron. Bleach is an oxidiser. Pouring it on sets the stain harder and can turn a light orange mark into a stubborn brown one.
The correct product is acidic — a dedicated rust and lime remover, or oxalic or citric acid. Turn the water off at the stop, flush to empty the bowl so the cleaner is not immediately diluted, apply, leave for the full contact time on the label, then scrub with a nylon brush and flush.
Do not mix cleaners. Acid plus bleach produces chlorine gas, and a bathroom is a small room.
A pumice stone, used correctly
For hard mineral rings, a pumice stick made for toilets works on vitreous china provided both the stone and the surface stay wet the whole time. Keep it wet and use light pressure. Dry pumice, or pressure, scratches the glaze — and once the glaze is scratched the bowl stains faster than it ever did, because the roughened surface holds deposits.
Never use pumice on a coloured or enamelled tub, a sink, or any coated fixture.
Work out where the iron is coming from
- Every fixture stained, and the laundry too? Iron in the incoming supply. Common on private wells and not unknown on some municipal supplies in this region.
- Only the toilet, and only at the waterline? More likely mineral scale plus bacteria at the water surface than dissolved iron.
- Only hot water fixtures? Suspect the water heater — a corroding tank or a spent anode rod sheds iron into the hot side only.
- Started suddenly after works nearby? Disturbed mains sediment. Often settles in a few days.
Stopping it rather than scrubbing it
If it comes back within a week you are cleaning a symptom on a schedule. A whole-house iron filter or a softener with iron removal handles it at the source. Get the water tested first — the treatment for dissolved ferrous iron is not the same as for iron bacteria, and buying the wrong system is an expensive way to keep the stain.
One thing not to do
Do not drop an in-tank bleach or blue tablet in to keep on top of it. Beyond making iron staining worse, those tablets sit against the flapper and the tank seals and degrade them, which is how you end up with the running toilet from an earlier post.