Laboratory research has shown that when phosphate is removed from the water, algae growth is impacted. In such situations, reason dictates, it is much easier to control with EPA-registered algicides — chemical compounds such as chlorine, bromine, quaternary ammonia compounds, poly quats, copper and silver. With less algae to deal with overall, a registered algicide, along with a good sanitization program, can be more successful in keeping pool water clean and clear.
It's helpful to think of algae separately from other pool invaders such as bacteria. In many cases, pool professionals lump them together and rely on chlorine to be the sanitizer as well as the oxidizer and algaecide in the pool. Because chlorine can be an EPAregistered algaecide, the mindset is that additional algaecide is not needed. Let's consider something, however. What is chlorine's No. 1 job to do in a pool? It's not to kill algae. Chlorine's No. 1 job is to kill bacteria. To do that, there needs to always be a 1 to 4 ppm free available chlorine residual in the water.
If chlorine is asked to do the work of killing bacteria and preventing algae, more chlorine will be necessary to maintain the residual. Chlorine doesn't have a priority list to follow. Consider the number of times a pool is tested on a weekly basis and the chlorine residual is 0 ppm. When this occurs, the pool does not have any protection against algae or bacteria, and algae can grow and reproduce quickly.
The use of a preventative algaecide on a weekly basis is one of the best products you can incorporate into weekly pool care to make your pool maintenance programs as effective and efficient as possible. Adding a preventative algaecide, such as a blended formula, copper-based algaecide, or a quat- or polyquat-based product, will provide protection against algae even if the chlorine residual is lower than acceptable. Keep in mind that algaecides do not protect against bacteria; a free chlorine residual is essential to kill bacteria and allow for swimming.
ROLE OF PHOSPHATE IN ALGAE GROWTH
There is nothing that will replace the need for an EPA-registered algaecide as part of regular pool maintenance. However, a look at how algae utilize nutrients they have access to can give us some options for making pool care programs more efficient and less likely to lead to water quality issues.
Let's examine the critical nutrients for algae. Like human beings, algae need a balanced diet of nutrients to be healthy, strong, and able to reproduce to create an algae bloom in a pool. What happens to algae if we limit one of those food groups? Let's apply the scientific principle called Liebig's Law of the Minimum. This Law says that if you limit one factor that's necessary for growth, then you're going to limit the overall ability of the system to grow. The system can survive but will not be as healthy or strong as possible, which may limit growth and reproduction. Nitrogen, phosphorus, magnesium, and other trace minerals are the critical food groups that algae need to be able to grow, reproduce and be healthy.
According to Liebig's Law of the Minimum, algae can only grow as strong as your weakest link. What happens if one or more of the nutrients that algae need to grow in a pool are limited? Is algae cell yield or ability to reproduce diminished? Let's focus on phosphate, which is a crucial nutrient for algae, as well as something we can test for, remove, and manage in pool care. Applying Liebig's Law of the Minimum can illustrate how limiting phosphate availability can create a system where the amount of algae is easily controlled by using a preventative algaecide.
Experimental Insights: During extensive algae research at Biolab, Inc, we set up controlled environments varying in nutrient composition to highlight phosphate's significant role in algae reproduction, as well to explore the impact of magnesium, nitrogen, and other nutrients on the health of algae. Samples were set up by adding a common form of green algae to a growth medium that contained all the elements that algae need to grow, minus one critical nutrient, which differed for each sample. The control sample had all the critical nutrients necessary for algae growth and reproduction.
In one environment, all nitrogen was omitted, in another the phosphorus, and in the third bottle, all of the magnesium was omitted. In the last experiment, excess calcium was added to the growth medium.
The control sample after 20 days of growth.
The sample with phosphorus missing from the medium.
Here is the picture of the control sample after 20 days of growth [top photo above]. It had every nutrient it needed in excess to grow, reproduce, and be healthy. As you can see in this picture, it is healthy. When examined under the microscope, this sample was full of healthy cells that were actively reproducing and growing. Algae, with access to all nutrients it needs, will be able to grow and reproduce unless something is done to stop it.
This picture illustrates the sample with phosphorus missing from the medium [bottom photo above]. All other nutrients and parameters were identical to the control sample. Out of all the nutrients tested, phosphate is the one that can be tested, removed and controlled in a pool environment. This bottle looks much different from the control. To be clear, the algae is not dead, it was just not able to grow as quickly. By itself, removing phosphate is not an effective method to kill or prevent algae. Removing phosphate will help, but other means are necessary to ensure the objective.
These algae, with limited access to phosphate, are not reproducing at the same rate as the control sample. Under a microscope, the healthy algae cells are less prevalent, and signs of reproduction are not as evident. It is not growing as well as the one with all the nutrients. Which scenario would be easier to control with regular weekly pool maintenance? Is it the control sample with active growth and reproduction, or the sample with less growth present to kill? To be clear, if these bottles also maintained an appropriate sanitizer residual and utilized a preventative algaecide, algae growth would not be observed regardless of the phosphate, nitrate, or other nutrient levels.
PHOSPHATE REMOVAL
By removing phosphates from the pool environment, pool care becomes easier. The pool water is less likely to end up turning green overnight or to experience a recurring problem with algae.
Ideally, phosphate levels should always be less than 125 ppb in pools. This can be a difficult task, as phosphates are constantly introduced to pools from a wide variety of sources, including the environment, lawn care chemicals, rainwater and some products, just to name a few. The constant re-introduction of phosphate to pool water means that incorporating phosphate removal into part of a weekly pool care program is the best approach to keeping levels low. Most phosphate removers perform one of two functions: High-level phosphate removal or lowlevel maintenance removal.
High-level phosphate removers, which utilize the pool filter for removal, can remove high levels of phosphate in short periods of time. Expect temporary clouding of the water and the need to rinse or backwash the filter as part of this process. This is unavoidable because the only way to remove phosphate is to force a reaction that pushes it out of solution. At high levels of phosphate, a large amount of precipitation is expected which can temporarily cause cloudiness until it is trapped in the filter. However, once phosphate levels are below 500 ppb, weekly or routine maintenance phosphate removal products can remove low levels of phosphate to prevent levels from becoming high and causing problems. Weekly phosphate removal can be blended into multifunctional maintenance products that may contain the benefits of enzymes and clarifiers along with phosphate removal.
CONCLUSION
Algae control in swimming pools demands a multifaceted approach integrating regulatory compliance, chemical intervention, and nutrient management. By understanding the role of essential nutrients like phosphates in algae growth and employing targeted interventions in addition to the weekly addition of an EPA-registered algaecide and sanitization program, pool operators can effectively prevent and manage algae outbreaks. And that will help them effectively manage their pools.
This article first appeared in the September 2024 issue of AQUA Magazine — the top resource for retailers, builders and service pros in the pool and spa industry. Subscriptions to the print magazine are free to all industry professionals. Click here to subscribe.
