Spa tiles "bathtub ring"

[tpribors]

Our spa is integrated with the pool. The tiles at the top have gotten a "bathtub ring" that cannot be removed. At first I thought it was a calcium buildup but it doesn't react to anything I can think of.

1. Acid (relatively strong solution) to cut it. No success. The acid does react with the calcium buildup in the grout but the discoloration on the tile does not react.
2. I've tried abraisives. Scotch Brite scrubbing pads and even sandpaper. No effect.
3. The guy at our pool place suggested a small test area with CLR. No effect.

The rest of the pool tile does not show this, at least to this degree.

The regions have no "boundary", that is if you rub your fingers on it from top to bottom the tile surface doesn't feel different

 

[ajw22]

Those tiles do not look shiny glazed. I think the tiles are unglazed or stone and the ring is etched into the tile surface.

 

[tpribors]

They are glazed ceramic tile. But I'm also certain that they've become etched... Even though I can't feel it it is impervious to chemicals so it has to be the surface itself...

Lesson learned from pool #1: Don't get dark tile or dark grout.

 

[mknauss]

Have you tried a magic eraser or something like simple green? That does not look like calcium, looks like sunscreen, hair product, etc.

 

[tpribors]

Yes. I tried CLR. It didn't affect it either. . It's not organic - there are no sunscreen or hair product (personal care materials) used in the spa. Like I said, it's not calcium since straight from the bottle (31%) muratic acid doesn't react with it. I've tried the abrasives like scotch pads and even 400 grit sandpaper. I was pretty tough on it with the pad but didn't want to get too far into the tile glazing with sandpaper.

It appears to be etching to me, yet there is no difference in the feeling of the tile surface.

I'm going to try some Vitamin C on the other "staining". I can expose that on a spa seat and just drain the spa without draining a portion of the pool. I'll try some on this too.