Toto Vespa Water Area Has Turned Yellow

[Tenderpaw]

The water area of my Toto Vespa with Sanagloss has turned light yellow. I have scrubbed it with Clorox toilet bowl cleaner several times and it will not clean up. Any suggestions that won't damage the Sanagloss? What could cause this?

Thanks,

Dave

[Terry]

I know in parts of Issaquah the water leaves a pretty good coating on bowls.
You may want to try CLR
http://www.jelmar.com/CLRbath.htm