The bathing fun is over when the pool water turns green due to poor pool maintenance. But what helps with a green pool, and what measures can you take to prevent the pool water from becoming green?
Green pool water is removed by scrubbing the pool with a pool brush and letting the filter system run for 24 – 36 hours with the addition of a flocculant. In the case of a mainly green pool, a shock chlorination with liquid chlorine and an algaecide is needed.
In this article, I will explain step-by-step how to clear green water in the pool and how to prevent cloudiness in the future.
How to fix (slightly) green pool water
Green water in the pool not only looks unsavory. It can also be harmful to pool owners and all other bathers in the worst-case scenario.
But I have good news: The murky pool water contaminated by algae can still be saved.
You don’t have to drain the pool water and refill the pool just because the pool has turned green due to increased algae.
All you need is the following pool equipment against algae:
- Pool net for coarse dirt
- A pool brush against the green debris
- Alternatively, a pool vacuum cleaner to suck off the algae
- Chlorine granulate or liquid chlorine for shock chlorination
- A powerful algae preventive (algaecide)
- Flocculants to improve the water filtration
- Electronic water tester for optimal water treatment
- A floater for the chlorine tablets
- Safety glasses and a respirator
I will show you how to clean a green pool with my tried and tested method.
If you only have slightly green water in the pool and the pool is partially milky, then the procedure explained below is ideal for cleaning the pool quickly.
If the pool is entirely green, I recommend jumping straight to the second procedure and taking harsh measures.
1. Thoroughly scrub affected areas in the pool
Quick action is required if the pool is only green in isolated places or has only slightly green water.
Typically, the shady corners and other dead zones in your pool are the first to be invaded by the green algae.
Take a pool brush and scrub these areas thoroughly.
I recommend using a soft pool brush for a liner pool or GRP pool. In a concrete pool, you can take a steel brush right away.
Some advisors recommend vacuuming the pool directly with a pool vacuum, but this is not always necessary.
If there is a lot of dirt on the bottom of your pool, you can vacuum the pool briefly before scrubbing.
Tip: The green algae pull its threads beyond the visible areas, and while you’re at it, it is best to scrub the pool over a large area.
2. Increasing the circulation time of the pool pump
After the pool has been thoroughly scrubbed, running the filter pump for a few hours is important.
Check the current transfer time and, if necessary, increase it to 8 to 12 hours a day.
Usually, the pool becomes visibly clear after a few hours.
I recommend running the filter pump continuously for 24 hours – provided the water parameters are correct. If the pool is still not completely clear, simply let the pump run for a total of 36 hours.
One indication that cleaning is on the verge of failure is when the green pool water turns milky.
This means that there is a shortage of disinfectants. We’ll make sure that doesn’t happen in the next few steps.
Extra tip: As long as the pool water is milky, adding approx. 5 liters of liquid chlorine is sufficient. The pump must then run until the water is clear again (typically 24 hours) and the chlorine content falls below 1.5 ppm.
3. Use a flocculant to improve the filtration
Use a suitable flocculant in the pool while the filter pump circulates the pool water.
A flocculant in the pool can significantly improve filtration. In my article, I will explain how to use the flocculant correctly.
Alternatively, you can find a recommended flocculant here.
My recommendation: Add the flocculant – preferably a flock pillow – to the pool immediately after brushing.
4. Use algaecide for safety in the pool
As already described, a lack of disinfectant in the pool can fail the cleaning work.
For this purpose, an algae destroyer (algaecide) is used, which also serves as an algae preventive.
The algaecide inhibits the formation of new green algae.
Info: If the algaecide foams when you use it, this is normal. You also have the option of using a non-foaming algae remedy – it’s a little more expensive but worth it.
5. Check and adjust the water values in the pool
In the meantime, when the filter pump is running, you should check the pH value and measure the remaining water values.
- The calcium hardness is between 200 – 400 ppm.
- The pH of the pool water should be between 7.2 and 7.6.
- The alkalinity is between 80 – 120 ppm.
If necessary, you can use test strips or, even better, an electronic water tester.
My tip: You can quickly optimize the pH level of the pool water with a pH plus or pH minus.
I also recommend using a floater and chlorine tablets to continuously produce free chlorine in the pool. Nothing works better in a green pool than chlorine.
This is how a totally green pool is cleaned
As already mentioned, the first method against green pool water is suitable for a light green pool.
If the water in the pool is tipped or the first method does not work, harsher steps are required to get the green pool water clear.
But don’t worry, you don’t have to empty the pool water here either.
1. Remove coarse dirt with the net
Take the net and use it – as far as possible – to remove the coarse dirt from the green pool.
Any dirt forms a food source for the green algae in the pool. Therefore, the dirt should be removed from the pool with a net every day.
In the worst case, the dirt in the pool is rotting and forms unpleasant gases.
You can recognize a rotting by the dead green algae that have turned brown over time.
A pool vacuum is used if the dirt is so fine that it cannot be removed with the landing net.
It is only important that you set the pump to empty when you suck the mud out of the pool with the pool vacuum.
You lose some pool water in the process, but you don’t want that stuff in the filter!
2. Shock your pool the hard way
In the second step, you don’t have to brush the pool, and you can go straight for a pool shock (also known as shock chlorination).
This step is essential if the whole pool is already green.
Wear protective goggles, and it is best to pour the liquid chlorine into the flow of the return nozzles – this is the best way to avoid splashes.
- With a chlorine content of 80 g/l, use 10 liters of liquid chlorine per 25 m³ of water.
- With a chlorine content of 150 g/l, use 5 liters of liquid chlorine per 25 m³ of water.
I recommend using the following pool shock.
Then the filter pump has to run for 24 to 36 hours and circulate what pool water. If necessary, the pump will also run longer.
Important! Bathing is not allowed during this time!
You can only use the pool again when the chlorine drops below 1.5 ppm.
Tip: If only the bottom of the pool is infested with the green algae, then you can only sprinkle the bottom with chlorine granulate.
Then let the chlorine granulate rest for 24 hours – with the pump switched off – and move on to the next step.
3. Thoroughly scrub the pool
While the pump is still running, muscle strength is required in the fight against the green monster (which you call your pool).
Scrub the pool extensively, and don’t miss any spots.
The shady places and the corners in the pool are ideal nesting places for the green algae.
Tip: During the entire 36 hours, you should always pick up the pool brush and scrub the surfaces in the pool.
4. Add a flocculant to improve the water filtration
Add a flocculant to the pool to improve filter performance.
Algae are very fine, and the flocculant can come in handy with filtration.
You also benefit from the fact that all other colloidal substances are also bound and filtered out in addition to the algae.
Check out the blog post for more helpful information on using a flocculant properly – I linked the post above.
5. Use an algaecide against this annoying algae
In addition to the flocculant, I recommend that you use an algaecide for better disinfection of the green pool water.
The algae agent actively combats the algae and inhibits their further spread in the pool.
But be careful: Do not use too much algaecide in your pool and always follow the manufacturer’s instructions.
Too much of the algae agent can be an additional burden for bathers as these agents are based on copper sulfate. This often turns the hair green.
6. Adjust the water values to a normal level
It is almost done after thoroughly scrubbing the pool and using all of the pool disinfectants I mentioned.
You now have to check the water values in the swimming pool and, if necessary, optimize them.
Using an electronic water tester is reasonable, as this is more accurate than classic test strips.
The values should look like this:
|Calcium hardness||200 – 400 ppm|
|pH Level||7.2 – 7.6|
|Alkalinity||80 – 120 ppm|
Check the water values while the pump is still running and improve if necessary.
After the procedure, your swimming pool should no longer be green but brilliantly clear.
What to do if the pool water is green and cloudy despite the chlorine?
If the pool water is green despite the use of chlorine, this is not necessarily due to the water treatment failure.
If the air suddenly becomes humidor after a thunderstorm, the green algae can quickly lower the pH level of the pool water and color the pool green.
For this purpose, the green algae nests on the walls and in the corners.
Just follow my instructions, and your pool should be clean again quickly.
- First, try to flocculate the pool to improve the filtration – you have probably not used a flocculant in the pool for a long time, or the filter medium is used up.
- Then set the pool pump permanently and extend the circulation time until the cloudiness of the water in the pool is removed.
- If there is still no improvement after the second step, I recommend changing the filter medium (sand, cartridge, etc.) – if the last change was more than 1 year ago.
Did you follow all of the steps, and the water in the pool is still green and cloudy?
If there is no improvement in the water quality, it can be assumed that some of the water will return to the pool unfiltered.
In this case, the multi-valve must be completely replaced.
But what if there was no change in the weather?
Another reason why the pool water is green despite chlorine may be that you are simply using too little of the chlorine.
Since chlorine is available in different dosages, I recommend not trusting the guideline values from any online pool maintenance guide.
In my instructions against green pool water, I explained how to dose chlorine.
Even after the pool shock, the pool water is still green. What to do?
It does happen that the pool water stays green even after a pool shock.
In this case, you have either bought a product with a low chlorine content, or the chlorine was – as already mentioned – incorrectly dosed.
Read through my instructions in detail above.
As a rule, after the shock chlorination, the pool should no longer be green if you have gone through all the steps.
I can only guess what is causing your pool.
You may have left out important spots while brushing, and the pool suddenly turned green again, or the pool filter run time is short because you are trying to outsmart the electricity provider.
Go through my instructions a second time and use the products I recommend.
Tip: I’ve published a complete maintenance plan on my blog on how to clean a pool to keep the water clean. Just follow the link.
Do you have any further questions about how to fix green pool water?
Contact me at @contactswimfool on Twitter, Facebook, Pinterest, and other popular social media – I’ll be happy to help you personally.
Have fun cleaning the pool water!