Why pools in Centurion and Pretoria turn green so fast
Algae spores are always in your pool. They arrive on the wind, on leaves, on swimming costumes and in rainwater. Chlorine kills them as they land. A pool turns green when, for a few days, there is not enough working chlorine in the water to keep up, and the algae multiply faster than the sanitiser can deal with them.
Gauteng summers are almost designed to cause that. Hot afternoons burn chlorine off in strong sun, and a late-afternoon thunderstorm then dumps rainwater, dust and organic debris into the pool, diluting what chlorine is left and pushing the pH around. A pool that looked fine on Friday can be cloudy on Sunday and green by Tuesday — especially after a long weekend when nobody was checking it.
Load-shedding and pump trouble make it worse. Algae thrives in still water. If the pump did not run its normal hours because of power cuts, a tripped circuit or a timer that reset itself, the water was not filtered and the chlorine was not circulated to the corners, steps and behind the ladder where algae usually starts.
- Not enough free chlorine after hot days or heavy use
- Rainwater and storm debris after a Highveld thunderstorm
- pH drifting too high, which makes chlorine far less effective
- Pump run-time cut short by load-shedding, a trip switch or a timer fault
- A filter that is dirty, channelled or overdue for a sand change
- A salt chlorinator cell that is scaled up and no longer producing chlorine
How green is green? The three stages we see
We price by pool size, not by how bad it looks, but the colour still tells us how long recovery will take. It helps to know which stage you are at before you call.
Light green or hazy: you can still see the floor, and the water has a tint. This usually clears quickly once chlorine is restored and the filter is running properly. Mid-green: the floor is faint or gone, the walls feel slippery and the steps have a film on them. This needs a heavy shock dose, brushing and several filter cycles. Dark green, brown or black-green: the pool has been neglected for weeks, often with leaves rotting on the bottom. This takes the longest and is the stage where a second problem is most likely to turn up, such as a failed pump or filter sand that has set solid.
What a green pool recovery includes
Recovery is not just pouring in a bucket of chlorine. Shock treatment kills the algae, but dead algae is still in the water and has to be removed, and the conditions that let it grow have to be fixed or it comes straight back. Our visit covers the whole chain.
- Water testing for chlorine, pH and alkalinity before anything is added
- Removing leaves and debris from the pool, weir basket and pump basket
- Balancing the pH first, so the shock dose actually works
- A shock treatment sized to the litres in your pool
- Brushing the walls, floor, steps and waterline to break up algae colonies
- Running and backwashing the filter, and vacuuming settled dead algae to waste
- A check of the pump, filter and chlorinator so we can tell you if anything caused it
Do you need to drain a green pool?
Almost never. Draining is expensive in water, wastes a resource Gauteng is often short of, and can damage the pool itself. An empty pool loses the weight of water holding it in place, and after summer rain the groundwater pressure underneath can lift or crack a shell. Fibreglass pools are especially at risk.
The only time we recommend partial draining is when the water chemistry is beyond correction — for example, stabiliser levels so high from years of stabilised chlorine that chlorine can no longer work properly. We test for that and will tell you plainly if it applies. For a normal green pool, the water can be recovered where it is.
How long does a green pool take to clear?
A light green pool is usually swimmable again within a couple of days of treatment. A mid-green pool typically needs a few days of continuous filtration and at least one follow-up vacuum. A black-green pool can take up to a week, because the filter can only process so much dead algae per cycle and it needs backwashing in between.
The biggest factor we cannot control is pump run-time. During recovery the pump needs to run far longer than its normal daily schedule, ideally around the clock for the first day or two. If your area is in a heavy load-shedding stage, plan the pump schedule around the outages with us so the filter is working whenever there is power.
Keeping it clear afterwards
A recovered pool will go green again if the cause is still there. When we finish, we tell you what we found: a pump running too few hours, a chlorinator cell that needs cleaning, filter sand that is past its life, or simply a chlorine routine that could not keep up with summer. Some of those you can fix yourself. Others are jobs we price on the spot.
A weekly maintenance plan after a recovery is the surest way to stop it happening again, particularly going into the December holidays. That is your choice — there is no obligation — but if you do, it starts from a clean pool rather than a green one. See our pool maintenance page for what a plan covers and what it costs.
How it works
Send a photo
WhatsApp 081 577 5051 with a photo of the pool, your suburb and the rough size. We confirm the price and a date.
Test and prepare
On site we test the water, clear debris and baskets, and correct the pH so the treatment works.
Shock and brush
A shock dose sized to your litres, then a full brush of walls, floor, steps and waterline.
Filter and vacuum
The filter runs long cycles and is backwashed; settled dead algae is vacuumed out to waste.
Report back
We tell you what caused it and what, if anything, needs fixing so it stays clear.
Frequently asked questions
How long does a green pool take to clear?
Light green usually clears within a couple of days. Mid-green takes a few days of continuous filtration. A very dark or black-green pool can take up to a week. The pump running long hours during recovery makes the biggest difference.
Do I need to drain my green pool?
Almost never. Draining wastes water and can damage the pool shell, especially after rain when groundwater pressure is high. We only suggest partial draining if testing shows the chemistry cannot be corrected.
Can I swim in a green pool?
No. Green water means there is not enough working chlorine to kill bacteria, and you cannot see the bottom, which is a safety risk for children. Wait until the water is clear and the chlorine and pH read correctly.
What causes a pool to go green overnight?
It is rarely overnight — the chlorine has usually been low for a few days. A hot spell, a thunderstorm and a pump that missed hours during load-shedding is the most common combination we see in Centurion and Pretoria.
How much does green pool cleaning cost?
It is a fixed price by pool size: R1,200 up to 30,000 litres, R1,500 for 30,000–50,000 litres and R1,800 above that. Repairs we find along the way are quoted separately.
Should I add chlorine myself before you arrive?
You can, and it will not hurt, but keep the pump running and the baskets empty — that helps more. Do not mix different chemicals in the same bucket, and let us know what you added so we can dose correctly.
Why did my pool go green again after I shocked it?
Usually because the dead algae was never vacuumed out, or the cause was never fixed: a pump running too few hours, a tired filter, or a chlorinator cell that has stopped producing. We look for the cause, not just the colour.