Yellow discoloration on tiles around spa

[JamesW]

Maybe hydrogen peroxide or a cleaner made specifically for stone.

Maybe limonene would work.

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Limestone and Travertine Floor Cleaner. Concentrated

Limestone and Travertine Floor Cleaner. Concentrated. Ph. Neutral. biodegradable and will not only safely clean and protect your natural stone surfaces

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Stain Proof SMC Peroxide Cleaner | S-Tech Stone & Masonry Cleaner

Stone & Masonry Cleaner specifically designed for cleaning stubborn organic stains and deeply embedded dirt in porous stone and masonry. Order or call now!

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[JamesW]

Maybe oxalic acid or TSP.

Note: Try on a hidden spot first to make sure that the product is safe to use on your surface.

Do you have extra stone from the original installation?

If yes, try on that first.

Always be careful with any chemical and start with a diluted solution first and increase the concentration as needed.

Do not use strong acids like hydrochloric acid.

Do not leave the product on the surface for a long time unless the instructions specifically say to leave it on.

https://savogran.com/pdfs/Wood_Bleach_MS.pdf

Stone Pro Oxalic Acid | Marble Polishing Products | Polishing Powder

StonePro Oxalic Aicd Powder is ideal for final polish for natural marble floors Restores. It also can be used on final shine to give your stone a new look. Shop today.

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[JamesW]

Wet Poultice Oil Stain Remover for Natural Stone Surfaces

Wet Poultice Oil Stain Remover - Wet Poultice is a topical poultice that pulls oil and water borne stains out of natural stone surfaces. 1

stoneproonline.com

 

[svho]

I am 99% certain the issue is sunscreen. The spa tiles colour came right during winter and now as soon as we start swimming again (with sunscreen on) this happens.

The only thing different in the water is bodies and sunscreen. PH, Alkalinity etc always fine.

It's a slightly sticky film. Gotta be sunscreen.

 

[JamesW]

Try Pool Perfect for cleaning.

Note: Get regular Pool Perfect, not a combo product.

Pool Perfect® - Natural Chemistry

naturalchemistry.com