Pool Algaecide Guide (Optimal Use to Kill Algae in Your Pool)

Beginners often use the algaecide in the pool, but the algae agent is not always necessary. When is the algaecide used, can it be harmful, and which agent would be an alternative?

Algaecides are used in the pool to remove algae and inhibit the recurring growth of algae. The rule of thumb is 1 liter of algaecide per 100 m³ of pool water, although the algae agent is not always necessary and can even be harmful to bathers.

In this article, you will learn the complete truth about pool algaecides and why you shouldn’t use them all the time.

What is an algaecide, and how is it used in the pool?

Algaecides are used to fight algae in swimming pools.

The algaecides sold in the US are ammonium compounds available in various qualities.

  • Not foaming
  • Slightly foaming
  • Strong foaming

Algaecides are available either as a liquid or processed as blocks in your local pool stores or online.

A well-known and frequently used algaecide is copper sulfate, based on heavy metals.

Heavy metals are harmful to health, but with the correct dosage of algaecide, bathers will not experience any allergic reactions or other side effects – you will find out how to do this below in the text.

Nevertheless, it would be best to be careful not to swallow too much of the pool water.

Under certain circumstances, using copper sulfate in a plastic pool can cause stains in the swimming pool.

The truth about the algaecide in the pool is: You don’t need the algaecide for pool maintenance.

Forums recommend the algaecide as an algae destroyer by an infestation with green algae.

Many beginners resort to the algaecide directly without informing themselves – In my instructions against green pool water, I explain how you can clean your water without algaecides.

Of course, the algaecide has some effect against algae, but it should not be used as an active agent against algae.

The algaecide is much more sensible to use as an algae repellent.

Tip: Read on in the article to learn more about alternatives to algaecides and preventive measures against algae.

How much algaecide to put in your pool?

But how is the algaecide used correctly in the pool to avoid allergic side effects?

As a rule, you should dose the algaecide according to the manufacturer’s instructions – As a rule of thumb, 1 liter per 100 m³ of water is poured into the basin every week.

Assuming the pool only holds 30 m³ of water, the formula is 0.3 x 1000 ml = 300 ml of the algaecide.

If you are unsure how much algaecide is in the pool, use the table with the quantities for using the algae agent as a guide.

Watervolume Algaecide
per 5 m³ 50 ml
per 10 m³ 100 ml

You probably wonder how the algaecide reacts in combination with chlorine or another disinfectant.

The question is: Can you apply the algaecide and chlorine together?

Do not worry. You can use the algaecide together with chlorine without any problems.

To increase the effectiveness of the algaecide, it is recommended to add 125 g of chlorine per 25 m³ of pool water – together with the algae agent.

Tip: You can pour the liquid algaecide directly into the return flow of the pump or dissolve it in a bucket beforehand and then use it in the pool – protect yourself from splashes on your skin.

How long is the waiting time after the use of algaecide?

And how long should you wait after using the algaecide before you can go back to the pool?

The waiting time depends on whether you only use the algaecide in the pool or whether you have also mixed in chlorine.

As a rule, it is sufficient for the filter pump to run for approx. 30 – 60 minutes before you can swim in the pool again.

Otherwise, your nails, clothes, or hair in the pool may turn green.

Incidentally, the green color often occurs when there is an overdose. Therefore, use the algaecide sparingly!

How do you measure the algaecide in the pool?

You are probably also wondering how to measure the algicide in the pool?

As already mentioned, you will notice an overdose of the algaecide on the green coloration of your hair, nails, and clothing – but it should not come to that.

Unfortunately, the algaecide cannot be measured with a simple test strip. It is strongly recommended to follow the dosage instructions for the algaecide.

When used weekly with the correct dosage, the measurement is not necessary.

Alternatively, you can use a modern water tester, which can even measure heavy metals in addition to the disinfectants, the pH value, and the alkalinity.

How to get rid of too much algaecide in a pool?

Beginners often use too much algaecide in the swimming pool or hot tub.

But, what to do if there is too much algaecide in the water?

Let’s assume that your hair on the scalp turns green due to an overdose of the algaecide, and the pool becomes cloudy.

In this case, the filter pump should continue to run as usual for 6 to 8 hours a day, and a part of the water should be replaced.

Take 30 liters of the pool water (per bather) a day – this will reduce the number of algae in the pool faster.

During this time, the water parameters (pH level, alkalinity, and disinfectant) are checked and, if necessary, balanced so that no new algae grow.

When to use an algaecide in your pool?

How the algaecide works against algae in the pool has not been scientifically clarified.

It is assumed that algaecides disrupt the normal cell processes such as cell division and the energy transport of algae, but we do not want to deal with that in more detail.

Much more interesting for pool owners is which types of algae in the pool and whirlpool can be eliminated and prevented with the algaecide.

So, when do you have to use an algaecide in your pool?

Fortunately, pool owners only have to deal with a few types of algae in the pool:

  • Green algae: Green algae are the most common algae in a pool. The green algae multiply rapidly despite good water values ​​when the weather changes. An algaecide is not necessary, but it can inhibit the growth of green algae.
  • Yellow algae: The yellow algae (also known as mustard algae or golden algae) are rare, but occasionally occur in private swimming pools.
  • Black Algae: The black alga (also known as blue algae) is dangerous and very difficult to remove from the pool. The use of an algaecide is therefore recommended.
  • Pink algae: In reality, there are no pink algae, and it is a slimy pink biofilm caused by bacteria. You can use an algaecide to inhibit the “pink slime” growth.

Under the links, you will find further information and step-by-step instructions against each algae species in the blog.

Do you need an algaecide in your pool?

The algaecide alone is not enough to combat algae and keep them away permanently from your pool.

This is because the algaecide only partially kills the algae and inhibits growth.

In the case of the dangerous black algae, a pool algaecide alone is almost ineffective. In this case, other measures are required to combat the algae.

The pool must be scrubbed with a pool brush to damage the cell walls of the black algae to improve the effectiveness of the disinfectant.

However, other measures are also required, which should be combined with the algaecide. You can read about them in the following chapter.

Pool shock against algae

No other agent is as effective in combating algae as chlorine.

To be precise, we are talking about shock chlorination (also called pool shock).

I have to mention that a pool shock is not always necessary.

In the case of partial growth of green algae or mustard algae, it is sufficient to scrub the pool, let the filter run for 24 hours and use the algaecide in the swimming pool to inhibit the algae from growing again.

However, if you have black algae in your pool, you cannot rely on the algaecide alone. In this case, perform a pool shock and apply the algaecide.

You can find out exactly how to do this step-by-step in my blog post about how to get rid of black algae in your pool.

Protection against algae when wintering the pool

When wintering the pool, in addition to the chlorine shock, the use of the algaecide can also be helpful to remove all algae from the pool.

Many do not know that the algae also grow in winter, just more slowly. Source.

Some advisors recommend rubbing the floor and walls with an algaecide after emptying the tank, as algae can grow in the winter on slightly damp and dry surfaces.

You can read how to use the algaecide when wintering the pool in the blog under the link.

Prevent algae in the pool without an algaecide

You now know how an algaecide works and when to use it. You have also learned that algaecides are not always necessary in the pool.

Aside from the fact that too much algaecide in the pool can be harmful, you also know that the algaecide has limited effects.

But what are the best alternatives to the pool algaecide?

  • Measure water parameter: Regularly test the parameter ​​in your pool with a water tester and optimize the levels, if necessary, with pH plus or pH minus. But be careful. Even with good water level, algae can grow if the filter run times are incorrect.
  • Production of free chlorine: With a dosing float and chlorine tablets, you can continuously produce free chlorine and thus counteract the growth of algae in the pool. With the correct dosage and constant values ​​of free chlorine, no algaecide is necessary.
  • Optimize filter run times: Algae grow most when the filter run times in the pool are too short. Turn up the filter runtimes and don’t try to save electricity in the wrong places with pool maintenance – under certain circumstances, you can adjust the nozzles to avoid dead zones in the corners.
  • Scrubbing the pool: Don’t neglect cleaning the pool with the pool brush. Scrub the pool regularly to loosen the still invisible algae and filter it out of the water with the filter system – in combination with a flocculant.
  • Products containing silver: Pool cleaners based on silver have a very disinfectant effect and, unlike algaecides, can be used without hesitation. The disadvantage is that they are a bit more expensive to buy.

Do you have any further questions about the pool algaecide?

Just use the search function or contact me at @contactswimfool on Facebook and Twitter with your question. I am happy to help you with the pool maintenance.

Have fun in the pool.

Photo of author
Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

Keep Reading