Quick Answers
Algae growth in swimming pools is caused by:
– Excess nutrients like phosphates and nitrates
– Inadequate chlorine levels
– Improper pH balance
– Lack of circulation and filtration
– Exposure to sunlight
– Warm water temperatures
Algae is a common and nuisance issue that plagues many swimming pool owners. The sudden appearance of green, black or mustard yellow spots in a once pristine blue pool is an unwelcome sight. Beyond just being an eyesore, algal blooms affect water quality, chlorine levels and can make swimming undesirable or even hazardous.
While algae occurs naturally in various water sources, swimming pools tend to be especially susceptible environments due to the water chemistry involved. However, with proper pool maintenance and quick corrective actions, algal growth can be prevented and controlled.
In this comprehensive guide, we’ll cover the factors that cause algae to grow in pools, the different types of swimming pool algae, as well as tips for removal and prevention.
What Factors Cause Algae Growth in Pools?
Algae spores are always present in the surrounding environment. However, they require favorable conditions in order to multiply and cause visible algal blooms. The main factors that contribute to algae growth in swimming pools include:
Excess Nutrients
Algae needs food to grow. In swimming pools, the primary nutrients are phosphates and nitrates. Some sources of phosphate and nitrate introduction into pools include:
– Fertilizer residue introduced by swimmers and pets
– Leaves, grass and other organic debris
– Runoff from gardens and lawns
– Swimmer waste like sweat and urine
Even very low concentrations of phosphates can trigger algal blooms. Most experts recommend phosphate levels be kept under 100 parts per billion (ppb) in pools.
Inadequate Chlorine Levels
Chlorine is a pool’s primary defense against algae. When chlorine levels drop too low, algae can take advantage and start growing rapidly. The ideal free chlorine level for pools is 1-3 ppm. Anything below 1 ppm for an extended time allows algae to gain a foothold.
Some reasons for low chlorine levels include:
– Infrequent testing and chlorine addition
– High swimmer load and chlorine demand
– New pool fills with low initial chlorine level
– Cyanuric acid buildup blocking chlorine effectiveness
– Extreme hot weather accelerating chlorine consumption
Improper pH Balance
Along with chlorine, the pH of pool water plays a key role in preventing algae growth. The ideal pH range for pools is 7.4-7.6. When pH strays out of this range on either side, chlorine becomes less effective at killing algae and microorganisms.
Low pH below 7.2 causes the water to become too acidic. This changes the ratio of hypochlorous acid to hypochlorite ion, making chlorine less effective as an algaecide.
High pH above 7.8 has the opposite effect, causing the hypochlorous acid ratio to decrease and inhibiting chlorine activity.
Lack of Circulation and Filtration
Your pool’s circulation pump and filter system play an integral role in circulating sanitized water and capturing contaminants. When water circulation is too low or filtration is inadequate, water quality and chlorine levels can drop, clearing the way for an algae invasion.
Potential causes include:
– Broken or undersized pump
– Clogged or damaged filter
– Leaks lowering water level
– Pump and filter run times too short
– Dead spots in pool with poor water mixing
Exposure to Sunlight
Most algae species require sunlight to thrive. Pools that receive more hours of direct sunlight are generally more prone to algae growth. Areas of the pool most impacted by sunlight like shallow ends and wall edges often see the most algal growth.
Outdoor pools have no control over sunlight exposure. But indoor pools can limit it by closing drapes and blinds during peak sunlight hours. The UV rays in sunlight fuel algae’s photosynthesis and growth.
Warm Water Temperatures
Algae prefer warm water for multiplying. Stagnant pool water that absorbs heat from the sun can reach bath-like temperatures of 85°F or more. This creates an ideal breeding ground for algal blooms.
Well-circulated water doesn’t heat up as drastically. Maintaining adequate water flow, running pumps on sufficient schedules, and checking pool temperature frequently helps prevent hot spots that are welcoming to algae.
Types of Swimming Pool Algae
There are several common algal species that grow in pools, each with their own characteristics. Being able to identify the type of algae present makes treatment easier. The main swimming pool algae types include:
Green Algae
This is the most common pool algae. It forms a thin, soft, green film on pool surfaces. An overgrowth takes on a thick, velvety appearance.
Green algae prefer warmer temperatures above 70°F. It mainly grows on walls and floors, especially in shallow ends where sunlight exposure is highest. Some strains cause distinctive black spotting.
Green algae are the easiest to treat with shock chlorination. It can be eliminated and controlled with proper chlorine and pH levels.
Mustard Algae
Also called yellow algae, this variety turns pool water a distinct mustard color. It has a fine, powdery appearance when rubbed between fingers.
Mustard algae is fast growing and able to thrive in low temperatures. It tends to form near pool bottom and on walls, giving a yellow, murky appearance to the water.
Mustard algae is more resistant to chlorine, but still treatable with shock dosing and brushing. It may require chemicals like algaecides to fully remove.
Black Algae
The toughest pool algae, black algae has dark green or black coloration. It grows in small, discrete patches that stick strongly to surfaces.
Black algae can thrive in all pool conditions – sunlight or shade, high and low temperatures, high and low chlorine levels. This makes it harder to prevent and eradicate.
Vigilant scrubbing, chemical algaecides and long-term chlorine levels above 2 ppm are needed to combat black algae’s resilient nature.
Pink Slime Algae
Also known as red algae, this species forms a slimy, reddish film on pool walls and floors. It has a jelly-like texture and tends to grow in warmer sections.
Like black algae, pink slime algae is tolerant of chlorine and can be controlled but not killed. It may require algaecides to remove and sanitize affected areas.
Diligent brushing of walls and floors helps keep pink slime algae from accumulating and spreading.
How To Remove Algae from a Swimming Pool
An algae invasion can happen surprisingly fast. But with the proper algae treatment process, you can get your pool clear again within a few days. Here are the recommended steps for eliminating algae from a swimming pool:
Test and Adjust Water Chemistry
Start by testing pH and sanitizer (chlorine or bromine) levels. Poor water balance creates ideal conditions for algae. Get pH between 7.4-7.6 and sanitizer level to the ideal range. This ensures maximum algaecide effectiveness.
Shock the Pool Water
Shocking raises sanitizer levels quickly to attack algae. Dose shock like calcium hypochlorite or sodium dichlor at 2-3x the normal amount. Run filter and circulation system continuously after shocking.
Brush Walls and Floors
Use a stiff pool brush to vigorously scrub affected areas. This helps dislodge algae growth so it can be killed and removed by the sanitizer. Pay extra attention to steps and walls which grow algae easily.
Use an Algaecide if Needed
Algaecides like polyquat 60 or sodium bromide give added algae killing power. They help destroy algal cell walls that chlorine has difficulty penetrating. Algaecide is most effective after shocking and brushing.
Clean the Filter
Run the filter for 24-48 hours to capture dead algae. Then clean or backwash the filter to prevent debris from reentering the pool. A clogged filter reduces circulation and sanitizer effectiveness.
Vacuum the Pool
Use your pool’s vacuum to suck up debris on the bottom. Removing dead algae cells prevents them from reseeding growth. Hand vacuuming with a hose may be needed for thorough results.
Maintain Proper Water Chemistry
Consistently maintaining balanced water and the proper sanitizer level prevents algae from returning. Test chemistry 2-3 times a week and brush walls regularly. Stay vigilant following an algae bloom.
How To Prevent Algae Growth
While removing existing algae is vital, prevention is ideal to avoid the issue altogether. Here are tips to help prevent algae growth in your pool:
Maintain Proper Sanitizer Levels
Keep chlorine or bromine levels in the recommended ranges of 1-3 ppm and 2-4 ppm respectively. Measure sanitizer daily or every other day. Top it up regularly, especially with heavy bather loads.
Balance pH
Check pH weekly and adjust to keep it between 7.4-7.6. This maximizes sanitizer efficiency and algae killing power. Acid lowers high pH, and soda ash raises low pH.
Shock Weekly
Periodically shock the pool even when algae is not present. This supercharges sanitizer levels to combat algae spores. 1-2x weekly shocking helps keep algae at bay.
Run Filter and Circulation
Maximize daily pump run times. Increase filtration turnover to 1-2x daily. Improve water circulation and suction issues. Proper water flow inhibits algae growth.
Use an Algaecide
Applying an algaecide like polyquat 60 1-2x a month boosts algae prevention. It helps destroy spores and growths that chlorine misses. Alternate use with shock treatments.
Reduce Phosphates and Nitrates
Control sources of nutrient input. Prohibit lotions, detergents or garden runoff from entering pool. Use phosphate remover chemicals to maintain low levels below 100 ppb.
Brush Regularly
Brush pool walls and floor weekly even when algae is not visible. This prevents growths from adhering and removes deposits that nourish algae.
Manage Water Temperature
Cooler water below 75°F slows algae growth. Limit direct sun exposure with covers, trees and structures if possible. Run pumps on cooler nights to mix in fresh water.
Clean the Pool
Remove leaves and debris regularly that decay into algae food. Keep covers clean. Check baskets and empty when full. Clean filter monthly or when pressure rises.
Conclusion
While no pool is completely immune from algae, following good maintenance practices can help reduce the risks substantially. Paying close attention to factors like chlorine, pH and phosphates creates an environment unfavorable to algal growth. Catching growths early before major blooms occur also leads to easier and faster remediation.
With the proper diligence and prevention regimen, you can minimize annoying and disruptive algal blooms, keeping your pool water clean, clear and ready to enjoy all season long. Consistency and vigilance are key – proper chemical balance, circulation and cleaning habits make all the difference in fighting pool algae.
