We are reader-supported. When you purchase through links on our site, we may earn an affiliate commission. Learn more.

Imagine waking up one day, stretching out slowly, getting up completely relaxed, raising the blinds, and then being startled to find that the pool has gone from crystal clear to a green, murky broth.

The reasons for this can be quite different.

During a vacation, you may have neglected pool chemistry, worn the same swimsuits unwashed in the pool after swimming in the lake, simply cleaned the pool too infrequently, or failed to remove debris in the pool.

Whatever the cause, now is the time to remove the algae.

An algae infestation can happen to even the best of us. There is no shame in it. Many would simply reach for the algaecide now. Sure, the name sounds promising, but is algaecide really the best way to get rid of algae?

The answer is: probably not.

What is algicide?

Algaecides are chemicals with an effect against algae, bacteria and fungi. Algaecides are used in the control and prevention of algae in swimming pools, on house facades and ships, and in cooling towers.

How Algicide Works

Many pool owners are unaware that algaecides are not an all-purpose weapon. However, if your pool is already infested with algae, there are more effective treatments to get rid of it. In practice, algaecides are used more as a preventative measure.

Algaecides are copper-based chemicals. Most commonly, copper sulfate or copper chelates are used as the active ingredient. Other algaecides are based on sodium carbonate peroxyhydrate or the herbicide endothall.

All of these chemicals attack the algal cells. Research has also not yet explained the exact circumstances of how the algaecides kill the algae cells. But the fact is that algaecides work – at least to some degree.

One problem is that most algaecides have a high metal content. This can be problematic for your pool if it already has a high concentration of metal. If this applies to you, you should choose copper-free algaecide.

Clorox Pool&Spa 43128CLX 42128CLX
If you click this link and make a purchase, we earn a commission at no additional cost to you.

Types of algae that are important to pool owners.

Of the tens of thousands of algae species, 99% of the time pool owners only have to deal with a few species. That’s just as well, because toxic algae species can cause fish kills and even enter the human food chain through the intermediary of shellfish.

Danger comes from non-toxic and toxic algae species. An example of dramatic consequences caused by non-toxic algae is the algae carpet off the coast of Brittany. This consists of the green alga Ulva lactuca, which is non-toxic. The algae carpets are washed up on the coast, where they dry out due to the sun and form a solid white crust.

Dangerous putrefactive gases from dead algae can develop under the crust. If people or animals step on the crusts, the toxic gases can be released. These become a health hazard if inhaled by humans or animals.

One worker has even died while removing the green algae. And it is suspected that his cardiac arrest was triggered by the toxic gases.

Fortunately, it doesn’t hit pool owners so badly. Pools are where you most commonly encounter these types of algae:

  • Green algae: Green algae is by far the most common type of algae in pools. They get into the pool when toys or swimwear are not thoroughly cleaned after a swim in lakes, thus carrying the algae into the pool.
    Green algae turn the pool water a greenish color. If the algae load is heavy, the hue is more intense.
  • Yellow or mustard algae: Mustard algae in the pool occurs less frequently, is more stubborn and difficult to get rid of.
  • Black algae: Black algae pose the most serious problems.

Balanced pool chemistry is the best weapon.

Algaecides tend not to be a means of algae control but prevention against algae. A much more effective means of fighting algae is chlorine (e.g. in the form of chlorine tablets). The classic disinfectant is perfect for ridding the pool walls of algae and making the water clear again.

Chlorine kills bacteria and algae and stops growth and decay processes. The chlorine content should be around 3 ppm. With other disinfectants such as bromine you can achieve the same goal, choose a bromine concentration of 3 to 5 ppm for this.

In a pool with a balanced pH and the appropriate level of disinfectant, you do not have to worry about algae growth.

HTH 22008 Ultimate Mineral
If you click this link and make a purchase, we earn a commission at no additional cost to you.

Shock chlorination for acute infestation.

If your pool is infected with algae right now, you need to shock the pool. Alternate between intense scrubbing of the pool and shock chlorination until the pool is clean again.

Algaecide can speed up this process, but it is not absolutely necessary.

We had previously addressed the different types of algae. In rare cases, you may be dealing with black algae or mustard algae. In these situations, you should rely on algaecides in addition to chlorine treatment.

HTH Pool Care Shock Advanced,
If you click this link and make a purchase, we earn a commission at no additional cost to you.

Preparation is the best treatment

In pool maintenance, regularity is the best remedy for almost any problem. In terms of algae infestation, balanced pool chemistry and a well-maintained pool are the best possible preparations.

As a complement to regularly cleaning the pool and maintaining pool chemistry, you must be careful not to unnecessarily introduce algae cells into the pool.

Reduce the likelihood of foreign objects getting into the pool water by thoroughly cleaning swimwear recently worn in lakes, rivers or the ocean before getting into the pool with it.

The same applies to swim toys, air mattresses, balls or other pool accessories. Disinfect them first and this way you will not bring algae into the pool unnecessarily.

Algaecides are an important preparatory measure. If children are in the pool or if you regularly swim in bodies of water, you should add algaecides to the pool water as a preventative measure to avoid algae colonization.

Algae blooms especially heavily in the summer. On a warm, sunny morning, a small dose of algaecide can reduce the likelihood of an algae bloom.

When winterizing the pool, algaecides are essential. Closed off with a winter cover, the pool creates a dark, moist environment where algae feels at home.

Read the usage instructions on the algicide package or manufacturer’s website and choose a dose of algicide accordingly when hibernating the pool.

Algicide is a useful agent used for hibernating pools, preventing algae infestations and controlling particularly stubborn types of algae.

In many cases, a balanced pool chemical is sufficient to keep the water clear and free of algae blooms. In the event of an infestation, shock chlorination will help. Many algaecides require you to shock chlorinate before adding the algaecide to the water anyway.

Larry has been a true water rat since childhood. Pure pleasure turned into a passion. That's why he is the first point of contact for friends and acquaintances when it comes to pool-related problems. He is an integral part of the PoolHandbook editorial team.