You touch down at Alicante airport, drive excitedly to your villa, and look forward to that refreshing first swim in your private pool. But stepping into the garden, your heart sinks: the sparkling azure water has transformed into a murky, emerald-green pea soup.
This is every Spanish holiday homeowner's recurring nightmare. Under the intense Mediterranean sunshine and high summer temperatures of the southern Costa Blanca, bacteria and algae proliferate dramatically faster than in Northern Europe. In this guide, we reveal why swimming pools tip so suddenly and how to maintain crystal-clear water year-round.
Once pool water temperatures exceed 28°C in July and August, algae reproduction rates quadruple. Concurrently, intense UV radiation destroys free active chlorine at record speed. Without stabiliser and sufficient filtration, pool water can turn completely green within 48 hours.
1. The Golden Triangle: pH Balance, Free Chlorine & Pump Runtime
A. pH Level: The Foundation of Chemical Balance (7.2 – 7.6)
When water turns cloudy, many homeowners simply dump extra chlorine granules into the skimmer. However, if your pH level is too high (exceeding 7.6, which frequently occurs due to the mineral-rich, hard municipal tap water in Alicante), chlorine loses up to 80% of its disinfecting capability!
- Target pH level: strictly between 7.2 and 7.4;
- Apply pH Minor (pH reducer) to restore the optimal band before adding sanitisers;
- Test chemical levels at least twice weekly throughout the summer months.
B. Pump Runtime: How Long Should the Filter Run?
A widespread false economy is attempting to trim electricity costs by running the pump for only 2 hours a day. Stagnant warm water is the ideal nursery for algae blooms:
- High Summer (June to September): minimum 6 to 8 hours daily, ideally split into two daytime filtration cycles during peak sunshine hours;
- Spring and Autumn: 4 to 6 hours daily;
- Winter: 2 to 3 hours daily is sufficient for water turnover and circulation.
2. The Spanish Phenomenon: Saharan Calima Dust
Several times a year, the Costa Blanca experiences a Calima: an atmospheric event where warm southerly winds carry dense clouds of reddish Saharan desert sand. Accompanied by rain, terraces and swimming pools are coated in reddish-brown clay dust.
Never vacuum fine Saharan sand through your standard filter setting! The microscopic clay particles will instantly clog your sand filter and blow straight back into the pool as a muddy cloud. Always switch your multi-port valve to WASTE / VACIADO (direct discharge to waste) when vacuuming calima silt off the pool floor.
3. Sand Filter Maintenance: The Regular Backwash (Lavado)
Every two weeks, the sand filter requires a backwash (lavado) cycle to flush trapped debris and dead algae into the drainage pipe. Run the backwash for approximately 2 minutes until the inspection glass runs clear, followed by a 30-second rinse (enjuague) before returning to standard filtration.
4. How to Rescue a Green Pool (Shock Treatment Protocol)
If your pool has already turned green, follow this systematic remediation routine:
- Adjust and lower your pH level to 7.2;
- Administer a Chlorine Shock (fast-dissolving granules) at roughly 15 to 20 grams per m³ of pool water volume;
- Add concentrated liquid algaecide (algicida) and place a flocculant tablet (floculante) in the skimmer to bind microscopic debris;
- Run the pump continuously on filtration mode for 24 hours;
- Vacuum the settled dead algae sediment from the bottom directly to Waste.
Enjoy a Pristine Pool Every Time You Arrive
Let our experienced pool technicians handle water chemistry, skimmer baskets, and backwashes. Your pool will always be pristine and swim-ready when you open your villa door.