Strange stain on tub shell, what is origin and how to remove?

[DangerBoy]

I have a '95 Hotspring Grandee with the standard Watkins white textured acrylic shell. I got it used and this last winter/spring was my first season with it, Over that first season, it developed a light orange to yellowy orange stain in a very small localized area abpve the waterline. The area where the stain appeared was along the inside ledge of the shell in the corner where I usually sit. When I sit there, I often put my arm up on that ledge and the spot where the stain has manifested itself is right where my armpit would be against the shell. The staining/discoloration hasn't appeared anywyere else on the shell. That's got me thinking that the discoloration may have something to do with an interaction between my chlorine based TFP chemical system and my aluminum based underarm anti-perspirant. That's all I can think of. Does that sound like a plausible explanation? Has anyone else ever had something like this happen?

I've got the tub drained right now and am doing some repairs and cleaning. I;ve tried scrubbing the stain out with a water and baking soda paste, a vinegar and baking soda paste, a borax and water paste and CLR. I think the baking soda paste helped remove the stain from the high points of the textured surface through abrasion but the stain still persists in the low points of the textured surface so it still quite noticeable. Can anyone suggest a product that should help to remove that stain chemically rather than through abrasion? Abrasion doesn't work too well in the recesses of the textured surface and I'd really like to get rid of the stain/discoloration.

 

[santacruzpool]

I used a magic eraser on my shell to remove some stains - might be worth a shot if you have any around...

 

[JamesW]

Try vitamin C. Dissolve some vitamin C in some water and use a rag to see if it works.

 

[DangerBoy]

Magic eraser: no effect. Vitamin C/Abscorbic Acid: no effect. TSP: no effect, Comet: no effect. Baking Soda paste with either vinegar or water: no effect.Goof Off: No effect.

Bleach maybe? Strong Acid or Base? I wish I knew a chemist.

 

[JamesW]

Do you have a picture?

 

[DangerBoy]

Here you go. The tub is kind of dirty becaust it's been drained for a while so most of the dirt and grime you see in the pics will be washed away when I give the tub it's cleaning. The lightly discolored area on the inside ledge where it's kind of light orange or yellowy orange is the area I'm talking about. Nowhere else on the entire tub got discolored like that and it wasn't that way when I got the tub and first put it into operation. The only thing that I can think of that differentiates that spot along the ledge from the rest of the entire ledge is that it comes into contact with my aluminum based anti-persperant from my armpits because I often sit in that corner and put my arm up on the ledge. I guess I should also mention that I also add my chemicals to the water in that corner but I always have the jets on when I do that and I add them to the water well out from the edge. You can't see it in the photo but there's a big powerful jet on the wall just below that spot so that would act to help push the chemicals that I add away from that ledge and cause them to mix further out away from that ledge.

The second photo is a close-up that shows how that the discoloration that's left after all my scrubbing is in the pores of the textured surface where the scotch-brite pad maybe doesn't reach too well. I'd sure like to know how to get rid of that discoloration and why it happened in the first place!

 

[JamesW]

Not sure what it is. Definitely odd.

 

[BravoRomeo]

Anti-perspirant does form a yellowish stearate when exposed to perspiration. That is the substance that both clogs your sweat glands and creates that funky yellow stain on your undershirts. Might be related?

Maybe try some diluted Ahh-some on it (follow their directions for mixing up spa shell cleaner).