Question about yellow in toilet bowl?

Everyday we have to clean a toilet in a house we are renting. There are two bathrooms and it’s only the one toilet on the main floor that does this. Basically the water is clear and stays clear, but over night the bowl (only where the water sits) turns yellow. It’s easy to wipe off, but I have no idea why or what... show more Everyday we have to clean a toilet in a house we are renting. There are two bathrooms and it’s only the one toilet on the main floor that does this.

Basically the water is clear and stays clear, but over night the bowl (only where the water sits) turns yellow. It’s easy to wipe off, but I have no idea why or what is happening.

My husband looked for rust and no signs of it. It doesn’t flush well, needing to hold the handle down and sometimes having to flush twice so I’m wondering if this has any relation.
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