Got Algae?

Aq 707 77pg 0001

Algae may be your nemesis, but you couldn't live without it. It is estimated that algae produce 73 to 87 percent of the net global production of oxygen. But it's still no good in pools.

Pinpointing the exact cause of an algae bloom can be difficult, since, according to Terry Arko, technical products specialist at SeaKlear, there are many things that can contribute to the growth of algae:

SUNLIGHT Algae have the ability to absorb light and, through photosynthesis, utilize light to convert nutrients like nitrates and phosphates to glucose energy. This energy is what empowers the algae to bloom.

LACK OF SANITIZER High bather load or an excess of organic debris in the pool puts a demand on chlorine. Excess nitrogen ammonia (from bathers) uses chlorine very rapidly. If the chlorine demand is not met, and there is not a sufficient residual of chlorine in the pool, algae can grow.

WARM WATER Most common pool algae love warm water. Algae can be a problem for many pools particularly in the spring, if, for example, a solar bubble cover is left on for an extended period of time. The solar cover allows the water to heat rapidly, and algae can grow as the chlorine residual goes down.

ROUGH SURFACES, CRACKS AND CREVICES Rough plaster or cracked surfaces and tile lines offer areas where many algae can gain a strong foothold. It is also difficult to reach into many of those areas with brushes, and so the algae are able to grow undisturbed.

POOR CIRCULATION Algae thrive in still waters. If pools have areas where the water doesn't move well, the result can be "dead spots" where algae can settle.

HIGH IRON CONTENT In October 2000, the scientific journal Nature published a study in which New Zealand scientists successfully initiated an algae bloom in the Southern ocean surrounding Antarctica by adding dissolved iron to the sea (National Institute of Water & Atmosphere 2000).

CARBON Carbon dioxide is what algae (and other plants) breathe and need to survive.

Ounce Of Prevention. . .

Of course, the easiest way to keep algae out of the pool is to prevent it. Pool industry experts agree the best way to avoid algae is to do the following:

1. Maintain a chlorine residual between 1 and 4 ppm at all times.

2. Continually add a maintenance dose of algaecide. Some are added weekly and others monthly. Directions on the product label will indicate how often and how much of the algaecide should be added.

3. Brush the pool walls regularly. "A lot of times when algae sticks to the surface of a pool, then it's a lot harder for algaecides and chlorine to get at it to kill it," says Ellen Meyer, technology manager for Arch Chemicals. "So if you brush it off the surface, you get it out to where those things can get in there and kill them. Then the dead algae bodies can be removed by your filter. So you definitely want to brush for any type of algae."

4. Make sure the filter is in good operating condition.

5. Keep water circulating effectively through every square inch of the pool so algae can't establish a foothold. John Puetz, vice president of research and development for Advantis Technologies, explains what to do to facilitate good circulation. "We want to make sure the return lines in the pool are directed in a generally downward direction," he says. "Oftentimes consumers like to turn eyeball returns up because they see a lot of movement of water at the top, and they think that's good. But the reality is that they need to mechanically force that water downward, so the return lines should be aimed gently downward and they should all be aimed in the same general circular pattern — either all to the right or all to the left — so that the water goes around the pool. If they have a main drain, at least one-third to 50 percent of their water flow should be through the main drain. A lot of people like to rely on skimmers, but the reality is the skimmers take care of the surface water. You need to mechanically force the rest of the water to move."


Exactly how you get rid of an algae bloom will depend on what type of algae it is and how big the bloom is.

Green algae are the easiest to treat. "If it's just a little bit of algae, then a regular shock treatment of 10 ppm of chlorine would be fine, and then you could follow that up with a more long-lasting algaecide, like a polymeric quat or just a regular quat," says Meyer. "If it's a little bit bigger of a bloom, then you might want to do 20 ppm of chlorine or double or triple shock it."

Puetz is not a fan of using high doses of chlorine to clear up these small to medium-sized blooms. "Normally speaking, high doses of chlorine are going to require some sense of rebalancing the water chemistry because they do tend to upset the water balance. Also, if I use a high dose of chlorine, I put vinyl at risk of bleaching, and I cannot swim in the pool when those high doses are present. Most algaecides are highly effective at killing green algae."

If you are faced with clearing up a pool that looks more like a green swamp, both Meyer and Puetz suggest first adding a flocculent to settle the bulk of the algae to the bottom of the pool, where it can be vacuumed off to waste. "Then hit it with a large dose of chlorine because then the chlorine doesn't have to work so hard," says Puetz. "The dosage you add is going to be far more effective.

"With mustard algae, keep in mind that it grows far more slowly than does green," adds Puetz. "That creates a challenge for any algaecide in terms of controlling it because the metabolic rate of the organism is slow, so its uptake of nutrients or anything that would kill it is also slow. So it requires that any algaecide you use has to reside in the pool long enough to be effective, but the kicker with mustard algae that is not true of green algae is it can survive in lowlight areas.

"So if you have a chronic problem with mustard algae — if it routinely comes back to the pool — then the next time you treat for it, not only should you add a good-quality algaecide, but at the same time, clean the filter. The reason to do this is because this organism like anything else in the pool is a suspended solid and will filter out, and a large number of these organisms can actually reside for extended periods of time in the dark areas of a filter. And the moment that the algaecide level or the chlorine level starts to drop in the pool, the algae can start to come back. So, oftentimes the pool is re-infesting itself. It isn't a matter of some service person that comes to the pool with a dirty brush and is infesting the pool from someone else's pool. This prescription of cleaning the filter after adding algaecide has been very effective at keeping the algae from coming back."

You may also want to try a product like Yellow Out or Yellow Rid. They are not algaecides, but used in conjunction with the appropriate amounts of sanitizer, can help to clear a pool of algae. If you are concerned about adding metals like the copper found in many algaecides to a pool, so if you have a chronic problem with mustard algae — if it routinely comes back to the pool — then the next time you treat for it, not only should you add a good-quality algaecide, but at the same time, clean the filter you may want to try this method.

"Black algae is actually a blue-green bacteria called cyanobacteria, though it does look like algae," says Karen Rigsby, technical sales specialist with BioLab. "What happens is it's surfaceclinging, so it tends to be prevalent in plaster pools because the surface is rough in texture. It likes to live in the grooves. You see it less frequently in vinyl and fiberglass pools, though you can get it there."

Beyond using chlorine and an algaecide specifically designed to get rid of black algae, you must brush it, though not for as long or as hard as you might think. "Black algae produce a protective coating on the outside of their little growth mats, and we need to brush that off in order to expose it to any chlorine or algaecide we're treating with," says Puetz. "Then brush the black algae spots on a daily basis after treatment has begun. That will get rid of the dead cells on the surface of the colony and expose living ones underneath.

"But you don't necessarily have to scrub it vigorously. The reality is it will brush off in layers, so patience is the key. Even though you may have to brush it once each day, you just need to brush over the area. You don't have to scrub at each little area for 20 minutes. And don't look to see substantial change in the appearance of the algae because you brushed it — just cover the area.

"It's critical to select an algaecide that says on the label that it's for black algae," continues Puetz, "because it'll contain a component that acts as a penetrating agent that will help pull that algaecide into any deeply set cells that are in the walls of the pool. All too often we miss that. We get the algae killed and brush it off the surfaces, but the reality is we haven't eliminated those cells in the wall and they just start to regrow as soon as they can."

Resistant Algae

Whatever type of algae it is, if it won't go away with the recommended doses of chlorine and algaecide, Rigsby says, "You might want to either bump up the algaecide or the chlorine. Go by label directions to determine how much to add."

To eliminate resistant algae, SeaKlear's Arko suggests using a phosphate remover: "We deal with thousands of service professionals out there who can attest that they're doing everything right in their mind: They're using algaecide, they're maintaining their chlorine, and they still have algae appearing in the pools. But when they reduce the phosphate, lo and behold, the algae goes away.

"We are in no way saying that you should not use an algaecide and chlorine for the treatment of algae," adds Arko. "We would not recommend a phosphate remover as an algaecide because it's not an algaecide — it's strictly to remove phosphate from water. When phosphate levels are maintained on the lower end, then your algaecides and your chlorine can work better at killing and keeping that algae out of the water."

Arko notes that algae can begin to thrive at phosphate test levels between 200 and 500 ppb, which is considered the midrange. "When levels reach 1,000 ppb, phosphate is high and resistant algae will be present."

If a pool doesn't have algae, there may be no need to use a phosphate remover, but in cases where you're using algaecide and chlorine and the algae is not going away, a phosphate remover, which helps remove the algae's food source, could be just the catalyst you need.

Cyanuric Acid: Your "Frienemy"

High levels of cyanuric acid (CyA) in a pool may also interfere with your efforts to eliminate algae. CyA acts a stabilizer that helps chlorine hold up better when exposed to UV rays, and if you want an outdoor pool to maintain a chlorine residual, it should have some CyA in it. However, in creating that stabilized environment, the CyA also slows the killing power of chlorine, according to Ellen Meyer, technology manager for Arch Chemicals. "We've noticed that pools with higher cyanuric acid levels have more difficulty with algae than pools with lower cyanuric acid levels," she says. "Chlorine is the thing killing things in your water. It's killing bacteria, algae, etc., and when you have cyanuric acid in the water, that chlorine spends some of its time attached to that cyanuric acid ring and some of its time as HOCl, hypochlorous acid, and it slows things down."

The National Swimming Pool Foundation CPO Handbook states, "For optimum chlorine protection, the cyanuric acid level should be maintained between 30 and 50 ppm. Many state and local codes limit CyA to not exceed 100 ppm." To lower the CyA level, you need to drain and refill the pool.

Buyer's Guide
Find manufacturers and suppliers in the most extensive searchable database in the industry.
Learn More
Buyer's Guide
Content Library
Dig through our best stories from the magazine, all sorted by category for easy surfing.
Read More
Content Library