5 Things to Know About Using Oxalic Acid on Pool Concrete Rust Stains

Oxalic acid is the standard for pool concrete rust stains It lifts rust without eating the surface, unlike muriatic or phosphoric acid, which are more aggressive on concrete and can mess with your water balance.

Use pool-specific oxalic acid, not hardware store versions Hardware store wood bleach may contain unknown additives that can harm your pool water chemistry.

Dilute the powder per label instructions, typically 1 part acid to 10 parts water Brush it onto the stain, let it sit 5–10 minutes, scrub, and rinse thoroughly.

Protect yourself and your pool Wear gloves, eye protection, and old shoes. Keep the pump running to dilute runoff, and test a small area first.

Deep stains may need a second application or an overnight poultice For stubborn stains from years of metal furniture, mix oxalic acid powder with water into a paste and leave it overnight.