Algae growth in swimming pools is a common issue that many pool owners face. If left unchecked, algae can quickly take over and turn a pristine blue pool into a green swamp. Understanding what causes algae and how long it takes to get rid of it is key to keeping your pool algae-free.
What Causes Algae in Pools?
Algae spores are always present in the air and water. When conditions are right, the spores multiply rapidly, causing visible algae blooms. There are a few key factors that contribute to algae growth:
Sunlight
Algae needs sunlight to photosynthesize and thrive. Pools that get a lot of direct sunlight are more prone to algae.
Stagnant Water
When pool water is not properly circulated, algae spores can settle and take hold. Dead spots in the pool allow algae to flourish.
High pH and Low Sanitizer Levels
Algae thrives when the pool water pH rises above 7.5 and the sanitizer levels (chlorine or bromine) are too low. These conditions provide the perfect environment for algae growth.
High Water Temperature
Warm pool water temperatures, typically above 80°F, accelerate algae growth. Higher temps combined with other favorable conditions can lead to swift algae blooms.
Nutrients
Phosphates, nitrates and metals like iron and copper found in pool water can act as fertilizer, feeding algae growth. These nutrients often come from external sources like fertilizer runoff.
Types of Algae Found in Pools
There are several common types of algae that can grow in swimming pools:
Green Algae
This hair-like green algae is the most common type found in pools. It spreads rapidly, forming a slimy, green mat on pool surfaces.
Mustard Algae
Also known as yellow algae, this powdery, mustard-colored algae colonizes slowly. It often appears after shocking the pool.
Black Algae
Black spot algae is dark and dotted and attaches firmly to surfaces like plaster walls. It is resistant to chlorine and is one of the hardest types to remove.
How Long Does It Take For Algae to Go Away?
If your pool has become algae-filled, you’re probably wondering how long it will take before it’s back to being clean and swimmable again. Here are some general timelines:
Minor Algae Bloom – 1 to 3 Days
For a minor bloom consisting of green algae spread over small sections of the pool, vigilant brushing and chlorine shocking can usually clear it up within a day or two. Make sure to scrub all areas thoroughly.
Moderate Algae Bloom – 3 to 5 Days
When algae has started to spread across larger areas of the pool and has formed some visible clumps or mats, it can take 3 to 5 days to fully rid the pool of the growth. Brushing and vacuuming daily, along with heavy chlorine dosing, are key.
Severe Algae Bloom – 5 to 14 Days
Thick, extensive algae that has turned the entire pool bright green often takes 5 to 14 days to eliminate. The pool may need to be shut down and given a heavy chemical treatment. Vigorous daily brushing of all surfaces helps remove the algae.
Super Stubborn Algae – 2 to 4 Weeks
In worst case scenarios where black algae, mustard algae or a severe growth covers the entire pool, it can take 2 to 4 weeks to completely clear. This requires draining part of the pool, thorough scrubbing of all surfaces, refilling, and potent algaecide treatments.
How to Get Rid of Algae
Removing algae involves attacking it from multiple angles:
Adjust pH and Alkalinity
Test and bring your pH down to 7.2-7.6. Alkalinity should be between 80-120 ppm. Proper pH and alkalinity impedes algae growth.
Shock the Pool with Algaecide
Using a concentrated algaecide containing polyquat, copper or enzymes works faster to kill algae than chlorine alone. Look for one suitable for your algae type.
Raise Chlorine Levels
Boosting the chlorine to 10-20 ppm quickly kills algae. Maintain levels at the high end of your pool’s normal range. The proper free chlorine level makes it very difficult for algae to take hold again.
Brush, Brush, Brush
Aggressive brushing of all pool surfaces every day with a stiff scrub brush helps loosen and remove the algae so it can’t regain a foothold. Pay extra attention to cracks and corners.
Vacuum the Pool Daily
Manual vacuuming combined with brushes are important for sucking up detached algae so it can be removed through the filter. Clean filters regularly during this process.
Add Flocculant
Using a flocculant or clarifier helps clump up any fine particles so they can be captured and filtered out. Flocculants make vacuuming algae more efficient and effective.
Consider Draining Partially
For extremely stubborn algae, partially draining the pool may be needed to rid it completely. Draining allows surfaces to be scrubbed more easily. Refill to dilute any remaining algae.
Be Patient
Depending on the severity, algae can sometimes take 10-14 days for total removal. Don’t give up too soon on the brushing, shocking and vacuuming routine before it has a chance to work fully.
How to Prevent Algae From Returning
Once you’ve finally managed to get rid of all the algae, here are some tips to stop it from coming back:
Maintain Proper Pool Chemical Levels
Keep chlorine level at the ideal 2-4 ppm range. Stick to the proper pH, alkalinity and calcium hardness ranges for your pool. Add cyanuric acid stabilizer to protect chlorine from sun degradation.
Shock Weekly
Using weekly shock treatments with potassium monopersulfate or chlorine helps maintain clean water and prevents algae regrowth. Shock more frequently during hot weather.
Reduce Sunlight Exposure
Covering the pool when not in use blocks sunlight penetration to discourage algae growth. Trim back overhanging trees to minimize shade lines where algae can thrive.
Inspect Weekly for Algae Spots
Check all pool surfaces for any small patches of new algae and treat immediately before they spread. Early intervention is key to prevention.
Use Algaecides Preventatively
Applying algaecides containing polyquats or copper a few times per month prevents algae from taking hold if chlorine levels drop.
Minimize Organic Nutrients
Don’t allow contaminants like leaves, fertilizer or dirt into the pool. They provide nutrients that enhance algae growth. Use enzyme products to break down organics.
Replace Pool Filters Regularly
Old, saturated filters allow algae to pass through rather than get captured. Swap out cartridge filters every 2 months and sand filters every 3 years.
Understanding Algae Growth Cycles
Algae reproduction follows certain growth cycles during the season:
Spring Growth Phase
When pool water temperatures reach 60°F, algae begins rapid reproduction as sunlight intensifies and chemical levels can be unstable after winter. Stay vigilant about potential blooms.
Summer Bloom Phase
Pools are most prone to major algae blooms in summer when temperatures climb over 80°F and sunlight is strongest. Growth happens quickly if chlorine drops.
Fall Resting Phase
As sunlight fades and water cools in autumn, algae enters a resting phase and blooms subside. However, it can still regrow if sanitation isn’t maintained.
Winter Inactive Phase
Freezing temperatures prevent algae reproduction and cause cells to go dormant until the following spring. But algae spores remain present, ready to bloom next year.
Common Algae Myths and Facts
There are some common misconceptions about algae in pools. Here are the realities:
Myth: Pool paint or tile color affect algae growth.
Fact: Dark plaster does not increase algae growth. Proper water chemistry prevents algae regardless of pool finish.
Myth: Lowering cyanuric acid helps kill algae.
Fact: Only chlorine actually kills algae. Cyanuric acid merely stabilizes chlorine from UV rays.
Myth: Surface skimmers remove algae.
Fact: Skimmers only filter fine debris from the water’s surface. Brushing and vacuuming are required to remove algae.
Myth: Salt chlorine generators stop algae.
Fact: Salt chlorinators still require maintenance of proper chlorine levels. Salt does not directly kill algae.
Myth: Algaecides provide long-term algae prevention.
Fact: Algaecides work short-term when added. Chlorine is still needed for ongoing algae prevention.
What About Clear Water And No Algae for 2 Months?
If your pool has stayed clear for 2 months with no algae blooms, here are some possible explanations:
Proper and Consistent Chemical Levels
Maintaining proper chlorine, pH and other chemical parameters prevents algae growth for extended periods if test and adjust regularly.
Added an Effective Algaecide
Using a quality algaecide with active ingredients like polyquats as part of regular maintenance keeps algae at bay for 1-3 months.
Consistent Pool Filtration
Running your filter daily for optimal hours circulates water thoroughly and filters out microorganisms consistently before they grow.
No Contamination Introduced
Preventing organic materials like leaves and dirt from getting into the pool reduces potential nutrients that feed algae.
Low Sunlight Conditions
Having lots of tree shade, a mesh cover, or closing it when not in use limits sunlight exposure needed for algae blooms.
Cooler Temperature Pool
Maintaining water temperature below 75°F slows down reproduction cycles of algae even with sunlight exposure.
New Pool Plaster Surface
The initial smooth plaster surface after refinishing leaves little space for algae spores to adhere and grow during the first few months.
Conclusion
Algae can appear and reproduce rapidly in swimming pools when conditions are ideal, creating green murky water. Getting rid of algae involves ensuring proper water chemistry, vigorous brushing and vacuuming, algaecides, and patience. Preventing algae from recurring means paying close attention to chlorine levels, shock treatment, filtration, and other regular maintenance. With a diligent regimen, your pool can stay sparkling blue and algae-free for months at a time.
