Archive for the ‘Tips’ Category

Color-coded Tips for Treating Algae in the Swimming Pool

Friday, April 28th, 2017

Algae Swimming PoolAlgae in the swimming pool is an unwelcome sight, but one that usually can be dealt with effectively. The following “color-coded” tips can help you or your pool service professional identify and eliminate, or at least control, the most common types of algae. It is important to follow manufacturers’ directions for using and storing all pool chemicals.

Green Algae

Green algae usually appears when pool sanitizer levels are low or water circulation is poor; green algae turns pool water cloudy and murky. It is the easiest type of algae to remediate, but left unaddressed, green algae can worsen to the point of obscuring the floor and steps of the pool and potentially even a struggling bather, raising the drowning risk. Eradicate green algae by raising the chlorine level or adding an algaecide. Following treatment, it is important to run the filtration system continuously to clear the water by trapping the dead algae in the filter.

Avoid green algae by maintaining proper pool chemical levels. Additionally, avoid cross-contaminating your pool with green algae spores by thoroughly washing swimsuits and water toys before re-using them in the pool following a visit to a natural water body.

Black Algae

Black algae appears as black dots on pool plaster, especially where the plaster is pitted, etched, or where calcium deposits have developed. Poor water circulation in those areas helps protect black algae. In fact, the more deteriorated the plaster, the worse the potential problem.

Tackle black algae as soon as it appears by scrubbing the affected area with a stainless steel brush. The scrubbing action removes a protective coating that develops over black algae. Daily brushing is required until the algae spots disappear. In severe cases, it may only be possible to control black algae, and not to eliminate it completely. It is essential to keep scrubbing black algae spots as soon as they appear.

An additional recommended step is to treat affected surfaces with “trichlor” on horizontal pool surfaces and a copper-based broad spectrum algaecide on vertical pool surfaces. Broad spectrum chelated copper algaecide can also be used as a preventative measure. A word to the wise: Have your pool water analyzed for metal levels prior to adding any metallic algaecide, such as copper-based products. If metals are present in the pool water, adding a metallic algaecide could cause the pool water to become oversaturated with metals, which could lead to staining or water discoloration. It is also advisable to keep copper to a minimum from a human toxicity standpoint. Most drinking water municipalities keep copper levels below 1.3 ppm. The manufacturers of copper algaecides should be able to provide the “ppm added” from use of their product. Excess copper in swimming pools can cause blue-green coloration of the hair, nails and skin.1

Yellow/Mustard Algae

Yellow or mustard-colored algae is probably the most challenging type of algae to eradicate. First, the diagnosis may be difficult. Yellow algae in a blue pool may look green, but the pool is not likely to contain green algae unless the water is cloudy and murky. Yellow algae may also be mistaken for dirt or pollen. The diagnostic test is to see whether or not the yellow substance returns to the side walls of the pool after it is scrubbed. Dirt or pollen will drop to the floor of the pool, but yellow algae will reappear on the walls.

To further complicate matters, yellow algae can thrive in a well-balanced chemically treated pool. It can be introduced into your pool from lakes, ponds, on the wind or in the rain. It can also be transmitted through previously contaminated pool equipment, such as skimmers, leaf rakes or vacuum hoses and heads. Treat yellow algae with an algaecide or chlorine enhancer that specifically targets yellow algae.

Anti-algae Basics

To help avoid algae of all types, keep in mind the basics of chemical and physical pool maintenance.

CHEMICAL MAINTENANCE: Proper pool chemistry means free chlorine and pH are within target ranges. According to the US Centers for Disease Control and Prevention’s Model Aquatic Health Code, pool water free chlorine levels should be in the range of 1-4 ppm and the pH should be between 7.2 (minimum) and 7.8 (maximum). The ideal pH in a pool is 7.4 to 7.6.

PHYSICAL MAINTENANCE: Physical maintenance of the pool means keeping up with brushing and vacuuming the pool and cleaning skimmer and pump baskets. Algae love rough and deteriorating pool surfaces, so sanding and crack repair are helpful. Clean pool filters as the first step in battling algae. Operating pumps and filters for at least 8 to 10 hours per day throughout the summer keeps water moving, a deterrent to algal growth.

This article is based on “Tips and tricks for identifying and treating tough algae,” by Terry Arko in the March 2017 edition of The IPPSAN, a publication of the Independent Pool & Spa Service Association, Inc.

Click here to download this article.

1 Peterson, J. et al. (2006). Cupric keratosis: green seborrheic keratoses secondary to external copper exposure. Europe PMC 77(1): 39-41. Abstract online, available:

Responding to Dengue Fever

Friday, October 9th, 2015
Responding to Dengue Fever

The female Aedes aegypti mosquito is the “vector” that transmits dengue fever from person to person.Image reprinted from the US Centers for Disease Control and Prevention website.

In the wake of recent monsoons and flooding, mosquito-borne dengue fever is once again on the rise in the Asia Pacific Region.  According to the US Centers for Disease Control and Prevention (CDC), worldwide, dengue fever cases number over 50 million annually.  The World Health Organization (WHO) estimates1 that globally 2.5 billion people, over one-third of the world’s population, live in areas that put them at risk for the viral disease, and about 70 percent of them (1.8 billion) live in the Asia Pacific Region.

Dengue is rare in the continental US, but endemic in Puerto Rico, where the CDC maintains a center of expertise and a diagnostic laboratory in its San Juan Dengue Branch.  It is also endemic to the Caribbean, Mexico and Central America.  According to the Gates Foundation website, dengue fever incidence has increased 30-fold worldwide since the 1960s.  Increasing urbanization and global travel contribute to ongoing outbreaks globally.

Dengue Fever Symptoms

Dengue fever symptoms range from mild fever to incapacitating high fever, with severe headache, pain behind the eyes, muscle and joint pain and rash, according to the World Health Organization.  Symptoms appear 3 -14 days after the infective bite.   The CDC advises patients to go immediately to an emergency room or closest health care provider if any of the following warning symptoms appear:

  • Severe abdominal pain or persistent vomiting
  • Red spots or patches on the skin
  • Bleeding from nose or gums
  • Vomiting blood
  • Black, tarry stools (feces, excrement)
  • Drowsiness or irritability
  • Pale, cold, or clammy skin
  • Difficulty breathing

Dengue hemorrhagic fever is a severe, potentially lethal form of the disease that generally requires hospitalization.  Children usually have a much milder form of dengue fever than adults, but those who survive the disease have a much greater chance of dengue hemorrhagic fever if they are subsequently infected as adults with a different serotype of the virus.

Avoiding Mosquitoes to Avoid Dengue Fever

Dengue fever is spread by the bite of infected Aedes aegypti mosquitoes, which are endemic to the southeast sector of the US among other world regions.  Humans are the reservoir of the disease, and there are at least four dengue viruses.  A person bitten by an infected mosquito may or may not develop symptoms.  That person cannot transmit the illness directly to others, but if a mosquito bites that person after he/she becomes infected, that mosquito can spread dengue fever to others through ongoing biting. According to the CDC, the Aedes aegypti bites primarily during the day. This species is most active for approximately two hours after sunrise and several hours before sunset, but it can bite at night in well-lit areas.

There is neither a vaccine for dengue fever nor specific antiviral medicines to treat the illness.  Preventing dengue is a matter of avoiding mosquitoes and their bites. Strategies include:

  • Eliminate standing water in flower pots, buckets, barrels, old tires, untreated kiddie pools and other containers that can serve as breeding grounds for mosquitoes.
  • Ensure good drainage of water around homes.
  • Maintain a chlorine residual of about 1 mg/l in stored treated drinking water; drinking water storage is common in developing countries that lack central water distribution.
  • Make sure backyard pools are appropriately chlorinated as mosquitoes will not breed in chlorinated water.
  • Inspect and repair window and door screens.
  • Apply an insect repellent to exposed skin and/or clothing when spending time outdoors. Products containing DEET, picaridin, IR3535, and some products containing oil of lemon eucalyptus and para-menthane-diol may provide long-lasting protectionfollow label directions for use.2
  • Apply insect repellent to skin after applying sunscreen, if sunscreen is to be used.
  • When you are outdoors, air movement around your body (from fans or natural breezes) disrupts mosquito flight and reduces your risk of being bitten.

The Indian Government is Activated

The Indian Express reports the current Dengue Fever outbreak is the worst one in five years, and notes other diseases with similar symptoms are also on the rise, including typhoid and B. coli.  The newspaper reports government inspectors go house-to-house in New Delhi in search of standing water, for even a few milliliters of clear water can become the breeding grounds of mosquitoes. Steep fines are imposed on residents who harbor standing water.  Fumigation is practiced in some areas.  Children are advised to wear full-sleeved shirts.

Government doctors have been told they will be on the job with no leave until the outbreak subsides and the number of hospital beds has been increased.

A High-opportunity Target

As flooding in the Asia Pacific region subsides, dengue cases are expected to decline.  Nevertheless, the disease remains one of the “most widespread vector-borne viral infections in the world,” according to the WHO.3  The Gates Foundation calls dengue fever a “high-opportunity target” because several potential vaccines are in development. The foundation supports efforts to develop a dengue vaccine, which it estimates could prevent more than 500,000 hospitalizations and 3,000 deaths annually, most of these among children (see press release).

An effective vaccine against dengue fever is the response we would most like to see to this global scourge.

Click here to download this article.

For more information on dengue fever and the Aedes aegypti mosquito, please see this CDC resource.

Ralph Morris, MD, MPH, is a Physician and Preventive Medicine and Public Health official living in Bemidji, MN.

1See: World Health Organization, Regional Office for South-East Asia, Asia-Pacific Dengue Strategic Plan (2008-2015)

2For more information on insect repellents and their effectiveness, please see

3WHO.  Dengue hemorrhagic fever:   Diagnosis, treatment, prevention and control. Geneva. World Health Organization, (1997): 12-23

Are you swimming in a healthy pool? Use your Senses!

Tuesday, June 30th, 2009

Sight: Look for water that's clean, clear and blue. Touch: Check for tiles that feel smooth and clean. Smell: Make sure there are no strong odors. Sound: Listen for pool cleaning equipment.

Pool Chemical Safety: Protect Yourself from Injuries

Monday, June 29th, 2009

A number of pool chemical-related health events have made headlines in recent months, including a chemical leak at a Las Vegas hotel-casino and a filter pump malfunction at an Indiana water park that sent two dozen people to the hospital. However, many more incidents never make the headlines. In fact, the Centers for Disease Control and Prevention (CDC) recently reported that as many as 5,200 emergency room visits per year are due to pool chemical–related injuries, and almost half of these injuries take place at home.

Pool chemicals help keep swimmers safe by killing bacteria and other germs that can lead to recreational water illnesses (RWIs). However injuries can occur in or out of the pool when critical safety rules for handling and applying pool chemicals are ignored. Inhaling fumes when opening pool chemical containers; attempting to pre-dissolve pool chemicals; and splashing chemicals in the eyes can cause injuries.

Fortunately, most of these injuries are preventable with proper chemical storage and handling practices. If you use pool chemicals, be sure to:

Always store chemicals as recommended by the manufacturer, and prevent them from mixing or getting wet;

Always secure chemicals away from children and animals;

Always read chemical packaging and manufacturer directions before use;

Always wear appropriate protective gear, such as glasses and gloves

Never pre-dissolve solid chemicals or add water to liquid chemicals; and

Never mix chlorine products with each other, with acid, or with any other substance.

While continuing its focus on preventing RWI’s caused by contaminated water, CDC is stepping up its efforts to prevent injuries caused by pool chemicals. To help spread the word to pool operators and backyard pool owners alike, we have developed a poster-sized check-list, which pool owners and operators can download or order for free by visiting Healthy Swimming Posters. This is another important tool to promote healthy swimming. Remember, healthy swimming is no accident!

Michele Hlavsa
Centers for Disease Control and Prevention