I use a scour stick from Walmart. https://www.walmart.com/ip/US-Pumice-Heavy-Duty-Scouring-Stick/772660938?wmlspartner=wlpa&selectedSellerId=11059&adid=22222222227253220826&wl0=&wl1=g&wl2=c&wl3=343266064308&wl4=pla-529908442759&wl5=9030453&wl6=&wl7=&wl8=&wl9=pla&wl10=125198037&wl11=online&wl12=772660938&veh=sem&gclid=EAIaIQobChMIsoH13_D25QIV7x6tBh01mga8EAQYASABEgIxBvD_BwE
I had tried everything, really everything, advertised to remove stains to get rid of that blue ring left by previous cleaning solution. Nothing worked until as a last resort I just added bleach to water in the bowl, left it overnight and stain was gone in the morning. Nice!
We have found limeaway to be a good product for this!
We have well water and get a crusty ring at the waterline that takes on a yellowish/pink tone. I have tried Limeaway... and it just ran into the water.... I did find CLR Kitchen and Bath spray.... it FOAMS up and sticks to the bowl above the waterline. I then used a heavy duty green scrubby to knock off the residue. I had to reapply the first go round...but once I got the main stuff off.... a weekly application keeps it off.
If yours is really thick you can try regular CLR.... turn off the water to the toilet, and flush it so the bowl drains below the normal waterline, soak an old towel (tear in half length wise) in CLR and place it on the crusty ring and let it set. You might want to duct tape the toilet shut... so someone in the family doesn't flush the towel down the toilet. I just tell my family that if they stop up the toilet.... THEY will be the ones to have to go after the clog..You can also use a pumice stone to help knock off any really heavy duty crust.
Lysol Lime & Rust Remover Toilet Bowl cleaner, comes in a black squirt bottle. Scrub with Scrub Daddy or Mr. Clean Magic Eraser. If stubborn, use a scouring stick to scrub.