If it were me, because I'm nuts, I'd replace the toilet no matter what because other people used it. But that's me because I'm cuckoo.

Abrasives like a pumice stone will leave scratches that will then stain easier.

The cleaning professional in me would first try bleach because that's what I have a lot of on hand.

If that didn't work I'd try hydrochloric/muriatic acid in an empty bowl.

BUT, and this is a big but, DO NOT use bleach and acid together, make sure you completely rinse any bleach you may have tried before the acid.

Also, open a window when using acid and do not use a brush or anything that could splash the acid on you. It won't kill you but it will tingle.

And wear safety glasses.

Try CLR. Then go back over with a pumice stone if this is still there.

Pop a couple of denture cleaner tablets in the bowl and let sit for 10 minutes then clean. It works, it got rid of the limescale on the bottom of my toilet bowl

Citric acid works well for limescale

Gotta get dirty to clean.

It's just an indicator to me if it's just something that is in an odd area which isn't being cleaned by the implements above, or if it's not something that's gonna ever come off.

Does it come off if you scrape it with your fingernail?

I had really bad hard water stains in my toilet..and I mean horrible. Use ZEP Acidic Toilet Bowl Cleaner

CLR toilet cleaner works well on this. After applying in the bowl and under the lip, let it sit for an hour or so then use a toilet brush. You may have to do this a few days in a row if it’s heavily calcified.

You can dip a sand paper into a mixture of powdered detergent and some liquid bleach and start sanding the area that you want to clean. Watch this

https://youtu.be/20sbpOYps2c

I suggest Cs Cleaner, watch this video: https://m.youtube.com/watch?v=2MC2ENo8uzI

Use white vinegar or a commercial lime remover to tackle hard water stains. Let it sit, scrub with a toilet brush, and repeat if necessary for a sparkling clean toilet bowl

CLR. Let it sit 30-1 hour, should get it all out. If some remaining no use a water soaked pumice stone. Do not use a metal device like a screwdriver or knife, they will scratch it

Its mineral build up so CLR, or Vinegar and it has to soak so you have raise the water level (block up the drain) or just keep toilet paper wet on the stains

Pumic stone! Will work best! Wet it thoroughly, and lightly start working it.. it won't scratch or damage your porcelain toilet

Did you try Lysol toilet bowel cleaner with bleach. That stuff is very powerful

CLR calcium lime rust. Let sit overnight and scrub with brush. To maintain after use comet cleanser and brush 2-3 times a week. This will work

This is what I use. My water has a lot of iron, so it turns everything rusty. This is the best cleaner I've found. It works on all hard water stains.

Borax. It is in the laundry aisle. Put it in the toilet and let it sit for a bit. Then scrub with a sponge.You may have to do it twice. It is powder and you don’t need to use much.

I've tried scrubbing it with thick bleach, letting bleach sit in it for hours, pouring coke in there and letting that sit and THEN scrubbing, I've tried baking powder in boiling water, letting it sit then scrubbing, I've tried "organic" type toilet cleaners. If anything it's gotten worse. How the fuck do I clean it?? It's embarrassing and annoying. I don't even know what it is, as it was like this when we moved in (in future I'm going to check the toilet of any house I'm thinking of moving into)

Pumice stone! SOS pads

Pool acid. It will sort it out but may affect your seals on pipes.

Had this problem - I let white vinegar sit in overnight after emptying the toilet bowl of water. After leaving it, it still required a good scrub but cane off rather easily and flaked off as I scrubbed. Used toothbrush, metal scouring pad and Stanley knife to push off areas that persisted from the edge after the initial bits had flaked off

I clean bars in an area that has VERY hard water. My favorite is pumice scouring stone from the hardware store. If you’re lucky you can get the kind on a stick lol. I have to wear gloves and stick my hand in the toilet.

Citric Acid. Powdered Citric Acid. Found at the supermarket. Sprinkle 1/4 teaspoon into water. Let sit overnight. No scrubbing. Repeat. 3 days shiny porcelain.

Whatever product you use, toilet bowl gel, Barkeepers, etc., I’d let it sit truly for a day. Let time + product do most the work!

First try using CLR (calcium, lime and rust remover).... you may have to buy a pumice stone for cleaning toilets - they're available at hardware stores and Amazon.

The Works USED to do it. Took off years of scale with zero scrubbing. But theychanged the formula, and it seems to no longer work so idk!

Lol, passive aggressive trolls and gatekeepers who have no reasonable argument as why not to try it?

Those folks aside, I hope it cleans up well for you.

You will need to do a strong acid soak overnight to remove the hard water ring. As for cleaning toilet I'd scrub it once a week. My favorite easy solution has been the Clorox magic wand.

I’d suggest scrubbing it with a wet pumice stone because it’s not gonna just go away, but once you do get the ring out you can use something like Zep acidic bowl cleaner to maintain.

Gentle scrub with a pumice stone should do the trick. Before I had a water softener I always had to do this about once a month. 

No. However, if you shut off the valve and then flush it and your toilet level doesn't come all the way up to the ring when you do that you might have some luck with something like CLR, but it's not going to do any good if it's diluted by the water in the bowl.

If you shut off the supply, you can sometimes get enough velocity with a plunger yo significantly empty the bowl. Depends on the p-trap.

You could also bail the water out. If you're especially squeamish you could put a bleach solution in there for a little bit so that when you do have to bail the next flush in order to get a product to work on the dry bowl, it would be sanitary.

I know this post is old but if you're still struggling to find something, Bar Keepers Friend Soft Cleanser worked very well for mine with minimal labor involved. Also, do you happen to know if your service line is galvanized steel? I have hard water as well but when my line ruptured and I replaced with PEX the water line marks completely stopped forming (even though I still have hard water). I know that's not a simple/cheap solution (or something to have done just for a clean toilet bowl!), I just wanted to throw that out there. I also used the BKF powder in the beginning as it's a bit more abrasive, so it got the bowl completely clean the first time (after I bought the house), but it was more cumbersome to apply, as I had to shut off the valve to the toilet and flush most of the water out to expose the bowl before sprinkling it on. Still, it did the job tremendously, and then I just used the soft cleanser periodically to keep the water line from reappearing.

I would fill the bowl with vinegar and let it sit overnight. Alternatively you can try CLR. Most people don’t let things sit long enough to let the product work for you. That’s probably part of the issue.

I say don’t use pumice! It scrapes off the coating and allows more staining.

A new toilet would probably be cheaper at this point

Step #1: Find a toilet distributor. Step#2: Find a landfill that accepts, umm, used toilets.

1 gallon of 93 octane and pack of matches will do it

I love the blue water in the toilet bowl. I just feel like it makes the toilet look cleaner

Amazon.com: Fluidmaster 8300 Flush 'n Sparkle Automatic Toilet Bowl Cleaning System with Bleach Cartridge : Health & Household

This bypasses the tank and goes straight into the bowl, it won't destroy your flapper and cause leaks. It is not bleach, even though it says it is...it uses bromine in the cartridge.

I personally like those gel stick-ons that attach to the inside of the bowl. Doesn't make the water blue and adds a bit of scent. Also adds a bit of suds to the flush so it functions a bit better.

I don't love fake scents at all, but I had a low flow toilet that was getting smelly like 2-3 days after cleaning -- so I just found the least flowery aroma I could. Right now I'm using one labeled "marine".

Not a replacement for actually cleaning the bowl on a regular basis (once a week, minimum.. or every other week if you have a smaller household), but fine to use to keep the bowl looking better in between).

NOTE: The following statement does not reflect my personal thoughts. It is a statement I heard from someone else.

I don't remember how it came up, but someone I knew once commented that he hates it when he goes to someone else's home and sees that blue color that some toilet tabs makes the water because it leads him to believe that the person doesn't clean their toilet at all and just relies on those tabs.

IMO, I thought that was really judgemental, but it was interesting to hear how some people might react or think if they saw that artifical color from toilet tabs in other people's homes.

Just a word of caution, some of those can cause issues with basically drying out the flapper and causing it to have to be replaced more often. If you don’t care about having to do that, then go for it.