Green Pool? Emergency Pool Cleaning in Ibiza

A green pool is one of the most common emergencies we deal with across Ibiza — especially at the start of season and after heat waves. Here's a straight explanation of what happened and how to fix it.

Why Your Pool Turned Green

Green pool water is almost always algae. Algae are present in every pool as dormant spores — they can't be completely eliminated, only suppressed. When the conditions favour them, they bloom rapidly. In Ibiza, this happens predictably:

• Free chlorine dropped below 0.5 ppm: Below this threshold, algae spores activate and begin multiplying. In Ibiza's UV intensity, an outdoor pool with no stabiliser can lose its entire chlorine residual in 2–4 hours of direct sunlight.
• Phosphates spiked: Algae feed on phosphates, which enter pools through leaves, Saharan dust, fertiliser runoff, sunscreen, and body products. A phosphate reading above 100–200 ppb creates ideal algae growing conditions even at adequate chlorine levels.
• pH crept above 7.8: At pH 8.0, chlorine is only about 20% effective compared to its performance at pH 7.2. A pool with "enough" chlorine on paper but a high pH can still turn green.
• Pump ran fewer hours than needed: In peak summer, an Ibiza pool needs 8–10 hours of filtration per day. A pump running 4 hours isn't turning the water over enough to maintain adequate sanitation.
• Pool sat unused for weeks: Low or no bather load combined with no service visits allows chemistry to drift and algae to establish. This is the classic cause of a pool that "was fine in June" turning green by the time owners return in August.

What the Colour Tells You

How to Fix a Green Pool — The Correct Process

There is a correct order to this. Doing it out of sequence wastes chemicals and adds days to the recovery time.

1. Test the water first. Before adding anything, test pH, free chlorine, alkalinity, and if possible phosphates. The treatment protocol is different depending on current readings.
2. Correct pH to 7.2. Chlorine shock at high pH is largely ineffective. Get pH down to 7.2–7.4 first using pH minus (sodium bisulphate or hydrochloric acid).
3. Brush all surfaces aggressively. Brush walls, floor, steps, and corners to dislodge algae from surfaces before shocking. Algae anchored to walls are protected from chlorine in the water column — brushing exposes them.
4. Apply a heavy shock dose. For light green water, 10× the normal free chlorine level (target 10–15 ppm). For dark green or swamp conditions, 20–30 ppm. Use calcium hypochlorite (granular) or liquid chlorine — not stabilised chlorine tablets (trichlor), which add excessive CYA at shock doses.
5. Run the filter continuously. Do not stop filtration during recovery. 24 hours continuous operation minimum. Backwash every 6–8 hours as the filter loads up with dead algae.
6. Add an algaecide. Once free chlorine is established above 5 ppm, add a copper-based or polyquat algaecide to kill any remaining algae and prevent re-growth. Do not add algaecide before establishing chlorine — it's ineffective in algae-bloom conditions without chlorine support.
7. Add a clarifier or flocculant if water is still cloudy. After the algae are dead, the water may be grey-green or cloudy from dead algae particulates. A clarifier coagulates fine particles so the filter can capture them. A flocculant (used in sand filter pools with a vacuum-to-waste setup) drops everything to the floor for manual vacuuming.
8. Final test and balance. After 48 hours of treatment and continuous filtration, retest all parameters and adjust to normal ranges before declaring the pool safe to swim in.

How Long Does Recovery Take?

Light green pool: 24–48 hours with correct treatment.

Established bloom: 3–4 days with professional treatment and continuous filtration.

Severe (swamp) conditions: 5–7 days, may require partial drain and physical scrubbing of surfaces.

These timeframes assume the equipment is functioning correctly and the treatment protocol is followed precisely. A pool treated with the wrong chemical order, or with filtration running only 4 hours a day, can take weeks and still not fully clear.

Preventing It Happening Again

• Maintain free chlorine above 1.0 ppm at all times — test weekly minimum
• Keep cyanuric acid (stabiliser) at 30–50 ppm — prevents UV from destroying chlorine
• Run the pump 8–10 hours per day in summer
• Test and treat phosphates if levels exceed 100 ppb
• Don't skip service visits during heat waves — high temperatures accelerate chemistry drift
• Brush the pool walls weekly even if the water looks clear