If your pool has turned green or gone cloudy overnight, you’re not alone. It’s one of the most common calls we get in Cyprus, especially after a long weekend, a stretch of 40-degree heat, or a Saharan dust event. The good news is that most green or cloudy pools can be rescued without draining. Here’s how it works and what to realistically expect.
Why Pools Turn Green or Cloudy in Cyprus
The short answer is algae, but the cause behind the algae is usually one or more of the following: chlorine that has burned off faster than expected, a filtration system that isn’t running long enough, or water chemistry that has drifted out of balance.
Cyprus makes all of these problems worse. The UV index here is among the highest in Europe. In July and August, free chlorine in an outdoor pool can drop by half or more in a single day if the water isn’t stabilised with cyanuric acid. Combine that with water temperatures regularly hitting 30°C or above, and you have near-perfect conditions for algae to take hold.
Hard water is another complicating factor. Cyprus has naturally high calcium and carbonate levels due to the island’s limestone geology. When pH rises, which it does quickly in hard water, chlorine becomes significantly less effective. A pool with a pH of 7.8 has roughly four times less active chlorine than the same pool at 7.2. So even if your chlorine reading looks acceptable, it may not be doing much.
Dust storms from North Africa, which arrive several times a year, introduce phosphates and organic debris that feed algae and cloud the water almost immediately.
How to Assess What You’re Dealing With
Before adding anything, test the water. Specifically, you need to know:
- Free chlorine level
- pH
- Cyanuric acid (stabiliser) level
- Calcium hardness
If you don’t have a reliable test kit, a basic dip strip won’t give you accurate enough readings for a rescue treatment. Take a water sample to a pool shop or call a professional who can test on site.
Cloudy but not green
Cloudy water without a green tint is usually a chemistry or filtration issue rather than a full algae bloom. Common causes include high pH, high calcium hardness causing precipitation, or fine particles the filter isn’t catching. Adjusting pH to around 7.2 to 7.4 and running the filter continuously for 24 to 48 hours often clears this up. A clarifier or flocculent can help bind fine particles so the filter can remove them.
Green water
Green means algae is present. At this point, adjusting pH alone won’t fix it. You need to shock the pool and address the root cause at the same time.
The Green Pool Rescue Process
Step 1: Adjust pH first. Shock chlorine is largely wasted in high-pH water. Bring pH down to between 7.0 and 7.2 before adding anything else. In Cyprus, this almost always means adding acid, typically muriatic (hydrochloric) acid or a dry acid product.
Step 2: Shock the pool. Use a calcium hypochlorite shock at a dose appropriate for the severity of the bloom. A lightly green pool might need 3 to 5 times the normal chlorine dose. A dark green or black-green pool can require 10 times or more. Add the shock in the evening to prevent UV from degrading it before it can work.
Step 3: Brush every surface. Algae clings to walls, steps, and corners. Brushing breaks up the colonies and exposes them to the chlorinated water. Don’t skip this step.
Step 4: Run the filter continuously. Dead algae and debris need to be filtered out. Backwash or clean the filter regularly during this period, because it will load up quickly. Depending on how severe the bloom was, this can take two to five days.
Step 5: Check and adjust stabiliser. If your cyanuric acid level is low, the chlorine will keep burning off before it can maintain residual protection. The correct range for an outdoor pool in Cyprus is generally 30 to 50 ppm. Above 80 ppm, the stabiliser itself begins to reduce chlorine’s effectiveness.
What If the Pool Doesn’t Clear?
If the water has been shocked and filtered for three or four days and is still murky, there are a few possibilities. The filter media may be exhausted or damaged. The phosphate level may be so high that it’s sustaining the algae despite adequate chlorine. Or the cyanuric acid level may have crept too high, a condition sometimes called chlorine lock, where the water tests positive for chlorine but the chlorine is largely inactive.
In cases of very high cyanuric acid or severe contamination, a partial drain and refill is sometimes the most practical solution. This isn’t always the first option, but it becomes necessary more often than pool owners expect, particularly in pools that have been left untreated through a hot summer.
When to Call a Professional
If you’ve done the steps above and the pool still isn’t recovering, or if you’re managing a holiday rental and need the pool presentable quickly, it’s worth bringing in someone who can diagnose the problem accurately rather than keep adding chemicals and hoping for the best. Mistreatment can damage pool surfaces, particularly plaster and certain liner types, and over-treating with algaecide or acid has its own risks.
We cover Limassol, Paphos, Nicosia, Larnaca, and surrounding areas. If your pool has gone green or you’re not sure what’s going on with your water, call us or send an email and we’ll arrange a visit.