Mineral build-up in only 1 of 2 toilets w/ photo

Hi everyone,
Many thanks to everyone for the help in my last post. I'm back with another dilemma. I have a problem with what appears to be a consistent mineral build-up in only one of my two toilets. I was told the problem is from the minerals in my water, but if that's the case, why is my downstairs toilet just fine and the upstairs toilet has a ridiculous build-up after two weeks? I took a picture of the toilet, and am going to attach. I know I can buy that CLR stuff, but to do that every 2 weeks seems ridiculous. O ye experts of the plumbing forum, please advise.
Thank you

It could be a number of things other than minerals from the water. If the toilet is used more often than the other or urine is allowed to sit in the bowl. Sometimes it could be s difference in climate from the downstairs to the upstairs (heat/cold, moist/dry air).
That little trail from the rim of the bowl may be a bacteria or mold/fungus.
Some will also say that if a toilet is frequently used by a member of the family that has a medical condition such as diabetes or maintenance medications are used long term, then the toilet will be affected with excessive staining.
How do the inside of the tanks compare to each other?
That's where you will also see evidence of build up that will be sent to the bowl. Especially if one tank is much older than the other.
Just throwing some ideas out there. Like I said, could be something other than hard water.

Have you ever used a pumice stone on that toilet? If not, give it a shot with regular weekly cleaning afterwards.