Zep Acidic Cleaner For Toilet's Blue Stain ?

Have that (typical) Blue stain in toilet.
Tried the Zep Commercial Acidic cleaner. Helped a bit, but not much.
Any other suggestions to remove this Blue stain that hopefully would work better ?
Must be a common problem.
Thanks, Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.