Domakihub How to Reduce Pool Phosphates and Keep Algae Out
Lower phosphate levels in five clear steps to protect your pool all season long.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
High phosphate levels are one of the main reasons Greek pools — whether at a private villa, a holiday rental, or a hotel — develop persistent algae even when chlorine looks fine on paper. Phosphates enter the water from fertiliser runoff, sunscreen, dust, and tap water, giving algae a constant food supply that chlorine alone cannot starve out. The video above from Leslie's Pool walks through the professional approach; the steps below give you a practical, Greece-specific routine you can follow yourself or hand to your pool technician.
Why Phosphates Are a Bigger Problem in Greece
Greece's long outdoor season, frequent Saharan dust events, and calcium-heavy tap water create ideal conditions for phosphate build-up. Irrigated gardens next to pool decks add fertiliser phosphates through splash and runoff, while guests' sunscreen and body oils raise organic phosphate loads every day the pool is in use.
The practical target is to keep total phosphates below 100 ppb (parts per billion). Above 500 ppb, algae can outpace even well-dosed chlorine; above 1,000 ppb, conventional shock treatments stop working reliably and you face repeated algae blooms that cloud the water and stain the liner.
Understanding Phosphate Removers
Phosphate removers are lanthanum-based products (sold under names such as PHOSfree, No Phos, or SeaKlear). They bind dissolved phosphates into tiny particles that your filter then traps and removes. They are not algaecides and they do not replace balanced chemistry — they simply eliminate the food source algae depend on.
Most removers are dosed by the amount of water and current phosphate level. A single treatment often brings a moderately elevated pool (200-500 ppb) back below 100 ppb within 48 hours, provided the filter is clean and running long enough to capture the floc.
How to Reduce Pool Phosphates: 5 Steps
- 1
Test your phosphate level accurately
Use a dedicated phosphate test kit or test strips rated for phosphate — standard 4-in-1 strips do not measure it. If your result exceeds 100 ppb, treatment is worthwhile. For readings above 1,000 ppb, plan two rounds of treatment a week apart rather than a single heavy dose, as very high concentrations can overwhelm the filter.
- 2
Balance your water chemistry first
Phosphate removers work inside chemically balanced water. Before dosing, adjust pH to 7.4-7.6, total alkalinity to 80-120 ppm, and free chlorine to 1-3 ppm. This prevents side reactions that reduce the remover's efficiency and avoids the remover clouding an already unbalanced pool.
- 3
Clean or backwash the filter
A dirty filter cannot capture the fine precipitate that forms when the remover binds phosphates. Backwash a sand or DE filter until the sight glass runs clear, or rinse a cartridge filter thoroughly. A clean filter also lets you shorten treatment time — plan to run the pump for at least 8 hours continuously after dosing.
- 4
Dose the phosphate remover according to your pool volume
Shake the bottle well, then add the correct amount directly in front of a return jet with the pump running. The water may turn milky or cloudy for 12-24 hours — this is normal and shows the product is binding phosphates into filterable particles. Do not swim during this period. For large pools (above 80 m³), split the dose into two equal portions added 12 hours apart.
- 5
Re-test after 48 hours and address the phosphate source
Run the pump for at least 48 hours before re-testing. If levels are below 100 ppb, the treatment is complete. If still elevated, repeat once. More importantly, identify and remove the source: trim fertilised plants away from the pool edge, ask guests to shower before swimming, check tap-water phosphate levels and consider an inline phosphate filter on the fill line if tap readings exceed 200 ppb.
Rather have a pro handle it?
Get a vetted pool pro in your city — one number, booked in EN/EL/DE.
FAQ
- How often should I test for phosphates?
- For an actively used holiday rental or hotel pool, test every two weeks during the swim season (May to October). For a private pool with low bather load, a monthly test is usually enough. Always test after heavy rainfall or periods of dusty weather, as both events deliver significant phosphate loads to outdoor pools in Greece.
- Can I use a phosphate remover with salt chlorination?
- Yes. Lanthanum-based phosphate removers are fully compatible with saltwater (saline) chlorinator systems. The remover does not interfere with the electrolytic cell. The only precaution is to balance pH and alkalinity first, because salt pools often drift toward higher pH, which can reduce the remover's effectiveness.
- Will removing phosphates stop algae completely?
- Eliminating the food source makes algae far harder to establish, but it is one layer of a balanced maintenance routine. You still need adequate free chlorine (1-3 ppm), a clean filter, and regular brushing of walls and steps. Think of phosphate control as raising the bar for algae — when combined with proper chlorination, it makes a bloom unlikely rather than just containable.