Algae is a pest that is commonly found in swimming pools all over the world. Even a pool that is correctly sanitized can still get an algae bloom when the conditions are right. But if your pool has algae how do you get rid of algae in a swimming pool?
Once you have algae in your pool it can be difficult to get rid of it. Sometimes the only way is to empty the pool, clean and refill.
As with most things in life, the prevention is better than the cure.
Follow a proper pool maintenance routine to test, chemically balance and sanitize the pool water to prevent algae growing in your pool. However, you need to take a few extra precautions to ensure algae doesn’t take over the pool.
You need to add algaecide at the beginning of summer to kill algae spores when they enter the pool water. This is like putting on sunscreen before going outside into the hot summer sun. It’s not a 100% guarantee that you won’t get algae but it’s another useful preventative measure.
You also need to shock the pool every week in the summer or after a period of high usage to kill excess bacteria, contaminants and algae.
Table of Contents
What is Algae?
Algae is an informal term commonly referring to a large and diverse grouping of unicellular bacteria (such as Chlorella and Cyanobacteria) and other micro-plants. There are literally hundreds of different species of algae-type micro-plants and unicellular microbes. The most common type of algae is green or yellow in color because they contain chlorophyll to photosynthesize light into energy and oxygen. These algae can rapidly reproduce from asexual cell division to take over your swimming pool water in a matter of days.
What Causes Algae in a Swimming Pool?
Algae growth in swimming pools can be caused by a number of reasons.
Climate
When the climate is warm, humid and sunny algae spores can rapidly grow in your swimming pool water. When spring and summer arrive your pool is in danger of an algal bloom.
Does rain cause algae in pool?
Yes. Wind and rain carry algae spores into the pool. Algae spores are commonly found everywhere in nature and will be blown by the wind into your pool.
Poor Water Circulation
Algae grows in stagnant water. Algae is less likely to grow on flowing water. Run the pool pump frequently enough to circulate the pool water three times or four times a day. I recommend setting the timer to run for 2 hours, three or four times daily. This will prevent the water settling enough for algae spores to grow in the pool.
Lack of Chlorine (or other sanitizer)
An adequate level of chlorine (or other sanitizer) will prevent algae from breeding in the water. If the chlorine level drops, for whatever reason, algae are given an opportunity to grow and take over the pool. Once algae have started to grow in the pool the normal level of chlorine will not be sufficient to prevent the algae from living in the water.
Poor Water Chemistry
Unbalanced water chemistry will reduce the effectiveness of your sanitation chemicals which give algae the opportunity to grow.
Read an article on Pool Water Chemistry
Poor Filtration
Dirty or worn out pool filters don’t effectively clean the water giving algae the opportunity to grow in the pool.
What temperature does algae grow in a pool?
Algae likes to flourish in warm water containing nutrients. Stagnant water and sunlight will accelerate the growth process. At temperatures lower than 60F and in lower light levels the growth of algae will be dramatically stunted.
Does covering a pool prevent algae?
Providing there are no algae spores in the pool a cover will reduce the likelihood of algae growing due to the lack of light. However, if algae spores are already in the swimming pool installing a pool cover is too little too late. It’s difficult to know whether algae spores are already in the pool. The pool water may be clear and the spores have not bloomed yet. If your pool water is dirty, unbalanced or low in sanitizer a pool cover will not fix the problem.
How to Prevent Algae in Pool
Algae can grow at very rapid rate quickly taking over your pool water and even clogging the filtration system.
It is important to take action immediately because if left untreated your pool will look like a swamp within a few days.
Untreated algae blooms only get worse and can cause black spots on the pool surfaces which are difficult to remove. The algae can take root into the walls of the pool causing micro-cracks and pitting of the surface. Algae will also grow in the pool plumbing and filter cartridge causing reduced water flow and less efficient filtration of the water.
Algaecide
One way to help prevent algae is to add algaecide to the pool water at the beginning of summer to kill algae spores when they enter the water. Algaecide is no the right treatment to get rid of algae in a swimming pool but is a preventative measure to prevent algae growth.
Shock the Pool
Another way is to ensure you shock the pool every week in the summer or after a period of high usage to kill any algae hiding in the water.
Clean the Filter
Regularly clean the filter. When the filter becomes clogged with debris the pump pressure increases and the water flow rate to the pump decreases causing the filter to become less effective at cleaning the pool water.
Replace the Filter Cartridge
Replace your filter cartridge every few years or when it has become worn or not able to be cleaned.
Clean Pool Equipment & Toys
Algae spores can hide on your pool equipment and toys. Clean the equipment so you don’t introduce spores into the pool water.
Run the Pump to Circulate the Water
Run the pump at least 8 hours daily in the summer. Set the timer to run the pump for 2 hours, 4 times per day. The extra circulation of the water will prevent algae taking hold on the pool surfaces.
What happens if you put too much algaecide in a pool?
Overdosing the pool with algaecide will not cause any serious issues. It will probably cause the pool water to foam and bubble especially coming from the outlet jets into the pool and around the skimmer box. After a while it will dissipate by itself.
How to Get Rid of Algae in a Swimming Pool
Brush the Pool to Get Rid of Algae in a Swimming Pool
If there is algae in your pool it will cling to the sides and bottom. Simply treating the pool water with extra chlorine will not necessarily remove algae from the pool surfaces. Brush the pool surfaces to move the algae into the water so that the filtration system can remove it from the water.
Vacuum the Pool Manually
After brushing the walls of the pool allow the algae to settle on the bottom. Then manually vacuum the bottom of the pool. Switch the water flow to the stormwater waste on your pump so you are vacuuming the algae into the drain. Otherwise, you will clog your filter with algae and you will need to clean the filter cartridge or backwash the filter unit to the drain. If your pool water level is too low after vacuuming add more water to the pool.
Don’t use a suction and robotic cleaner as it will not clean the pool well enough to get rid of algae.
Shock the Pool Water
The term “shocking your pool” means super chlorinating the pool water to a high dose of free chlorine that it is strong enough to kill algae and bacteria. This is the main weapon to get rid of algae in a swimming pool.
This is achieved by adding liquid chlorine or a granular dose of calcium hypochlorite shock treatment.
If the water is pale green a standard dose of shock treatment will be sufficient to clear up the problem.
However, the darker the pool water the more shock treatment will be required.
Medium green water requires about double dosage of shock treatment.
Darker green water needs a triple dosage.
Black spots and pink slime will require four times the standard dose of shock treatment.
Shock the Pool Water Again
It may take several days and multiple treatments, depending on the severity of the algae bloom, for the algae to die and the filter to clear up the pool water.
Add the shock to the pool in the evening so it won’t be affected by the sun and will have maximum effectiveness.
Run the filter until your pool water becomes clear. You may want to run it overnight. You will need to clean the filter during this process as it will become clogged with dead algae. Depending on your filter system, either backwash the filter or remove the filter cartridge and hose out the debris.
If your pool water is still cloudy the next day you can add a pool water clarifier chemical which helps to combine the small suspended particles in the water into larger particles that the filter can remove.
Once you pool water is clear again you can get back to a normal free chlorine level by returning to your routine maintenance and/or salt water chlorinator setting.
Test the water again and adjust your water chemistry if necessary.
Read an article on How to Clear Green Pool Water
How long does it take to get rid of algae in pool?
This depends on how developed the algae has become in the pool. If the algae is only growing in a few spots around the pool it can be cleared up very quickly. When an algal bloom has completely taken over the pool it may take a week to get rid of the algae.
Is algae in the pool dangerous?
No, algae will not harm you. However, if there is algae in the pool there will be bacteria, viruses and other contaminants which will harm you. Never swim in a pool with green water as it may cause health problems.
If you have algae you will most likely have water bugs that feed on algae. Larger water bugs that feed on the herbivorous water bugs will live in your pool. And these ones bite people.
Please read our article on How to Get Rid of Water Bugs in a Pool
Does leaving a pool cover on cause algae?
In a properly sanitized pool with chemically balanced water leaving a pool cover on will not cause algae to flourish. When your pool becomes chemically unbalanced and the sanitizer level falls algae will begin to grow. However, algae is known to develop resistance to normal levels of chlorine so you need to frequently shock (super chlorinate) your pool to prevent algae multiplying.
Do I use shock or algaecide first?
Do not add both pool shock and algaecide together into the pool. The two products will render each other chemically ineffective.
Algaecide is useful to add to a clean swimming pool to help prevent algae growing in the pool. Once there is algae you need to heavily shock the pool. Then many days later when the chlorine level has reduced add algaecide.
Drain the Pool Water to Get Rid of Algae
If the algal bloom is severe causing the pool water to become dark green and you are unable to see the steps in the pool it’s probably better to drain the pool, thoroughly clean it out with an acid wash and refill with fresh water rather than spending money on lots of pool chemicals.
Conclusion
Algae in a swimming pool is a very common problem among pool owners but it doesn’t have to be your problem. When you follow a good pool maintenance schedule, regularly test and balance your pool water chemistry you should never have to encounter algae in your pool. I highly recommend to maintain your pool because the prevention measures are much easier than having to eliminate algae from the pool.