How to Remove Calcium Stains From Pool Water
- Algaefree Australia Team
- 6 days ago
- 3 min read
Calcium stains can be an unwelcome surprise for any pool owner. Those white or grey chalky marks around waterlines, on pool walls, or along steps detract from the appearance of your pool and can damage surfaces over time if not properly treated.
At Algaefree Australia, we understand the frustration of dealing with stubborn mineral stains and offer specialised products designed for Australian pool conditions.
What Causes Calcium Stains?
Calcium stains typically form due to imbalances in your pool’s water chemistry, especially when calcium hardness or pH levels are too high.
Over time, minerals like calcium carbonate or calcium silicate can precipitate out of the water and adhere to surfaces.
There are two common types of calcium buildup:
Calcium carbonate: Appears as flaky white deposits. Easier to remove.
Calcium silicate: Forms greyish, hardened deposits that are more resistant and take longer to build up.
These stains are often caused by:
Evaporation (concentrating minerals)
Poor water balance
Hard fill water or bore water
Long-term neglect of water testing
Step 1: Test Your Pool Water
Before you treat the stains, it’s important to test your pool water and understand what’s causing the issue. Use a test kit to check:
Calcium hardness (ideal: 200–400 ppm)
pH level (ideal: 7.2–7.6)
Total alkalinity (ideal: 80–120 ppm)
These readings will help guide your treatment and prevent the issue from recurring.
Step 2: Choose the Right Treatment for the Type of Stain
Spot Stains
If you’re dealing with smaller, isolated marks, such as waterline buildup, rust spots, or stains from leaves, SPOTBLOC™ Stain Eraser is your go-to product.
This reusable chalk-like block contains a special blend of acids and is safe for all pool surfaces.
Instructions for use:
Rub a thin layer directly onto the wet stain
Can be applied above or below the waterline
Reapply as needed; the block lasts multiple uses
No need to adjust your water chemistry beforehand
SPOTBLOC™ is also effective for stains on stone surfaces around your pool.
Widespread Calcium Staining
For larger or more persistent stains, a whole-pool treatment is required. That’s where SeriouStain™ Remover comes in.
This powerful formula combines organic acids with chelating agents to dissolve calcium and other mineral stains without draining your pool.
Treatment instructions:
Prepare the pool
Lower the chlorine to 0 (chlorine interferes with the treatment)
Adjust pH to around 7 for maximum effectiveness
Turn off salt chlorinators and other treatment systems
Add SeriouStain™ Remover
Use 250g per 10,000 L of pool water for recent stains
For older or stubborn stains, double the dose and consider pre-dissolving hydrochloric acid to further lower the pH
Brush pool surfaces to help loosen deposits
Run the pump for a few hours daily during treatment
Most stains fade within 2–3 days
Restore Balance
Use sodium bicarbonate to slowly bring your pH back to 7.2
Replace at least one-third of your pool water if high calcium or mineral levels are ongoing
Step 3: Prevent Future Calcium Stains
Once stains are removed, it’s important to prevent them from returning. Regular water maintenance and ongoing treatment with SeriouStain™ Inhibitor can help.
SeriouStain™ Inhibitor:
Binds to dissolved metals and minerals to keep them in solution
Prevents future staining and scaling
Safe for all pool surfaces, including heated pools and bore-filled pools
Free from phosphate-based acids that can fuel algae growth
Ideal for use every 6 - 12 months
If your stains persist despite treatment, or if you’re unsure about handling pool chemicals yourself, we recommend getting in touch with a professional. Our team at Algaefree Australia can help you identify the stain, recommend the right treatment, and even connect you with trusted technicians. Explore our full range of pool stain removers on our website, or contact us for expert advice tailored to your pool.
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