Why Chlorine Is Not Killing Algae In Your Pool

Why Chlorine Is Not Killing Algae In Your Pool

Algal blooms are one of the serious problems that pool owners encounter. However, chlorine is one of the most effective ways to deal with this problem. Even though you have enough chlorine in your pool, you need to make sure that the free chlorine is up to 2 ppm and not more than 4 ppm.

Having a high total chlorine with low free chlorine makes your pool a wonderful habitat for algae and other microbes. What kills algae in your pool is the available free chlorine.

If you notice that the chlorine in your pool is no longer effective, it could be as a result of low free chlorine in the pool, which will require shock. It could also be as a result of the chlorine lock caused by the stabilizer in the pool. Read further to learn more about these factors.

Follow me in this article as I explain how you can use chlorine effectively to eradicate algae from your pool.

Can algae grow in a pool with high chlorine content?

One thing that is synonymous with swimming pools is algae blooms. Once the swim season starts, pool owners are regularly faced with this menace. Algae blooms are never welcomed in any pool as they make your pool unattractive to swim in. Apart from the aesthetics, algae can also form a home for bacteria, and this can lead to your pool being unsanitary.

No one wants to swim in a pool that is smelly or has that characteristic green look. However, having an algae outgrowth in your pool can be a threat to that. There are different kinds of algae, and some of these algae can have different reactions to chlorine. They include: green algae, black algae, and yellow/mustard algae.

  • Green algae: Green algae is the commonest form of algae found in pools. It is usually suspended in your water and is responsible for the haziness you see in your water. When green algae becomes quite prevalent, it can lead to very low visibility in your pool. It will make it difficult to see the steps in your pool.

This kind of algae is usually present when the sanitizer levels in your pool are low, there is a high pH or you have filtration issues. This kind of algae usually starts with mild cloudiness. But over time, it can become severe and you won’t be able to make out anything below the surface of your pool. Pool clarity is very important as it can heighten the risk of drowning.

However, this kind of algae is quite easy to kill. A good shock treatment and an infusion of chlorine can take care of this problem quickly. You can also add algaecide to the mix to help mop it up. The algaecide in this case will help to prevent the growth of new spores.

When using the chlorine shock. Ensure the other factors, such as pH and alkalinity levels, are adjusted properly. Also, ensure that your pool pumps are circulating effectively to ensure the shock is distributed evenly. If your filter is not functioning properly, then it might be time to change it.

  • Black algae: Black algae is quite a problem in gunite pools. They usually appear as black dots in your pool. This type of algae thrives in areas that have been etched or pitted. This etching is usually a result of calcium being leached from the walls of your pool. When these etchings occur, water might not easily flow into those areas. As a result of this, black algae can easily sneak in and thrive.

The problem with black algae is that they possess deep roots that can grow into your plaster. They also form an extra protective layer that makes them hard to eradicate. Because they usually require a place to hold on to, they are common where there are cracks in your walls and ladder rails. Most of the time, your regular chemical procedures might not work effectively on them.

To remove them, you must target their roots. Carrying out an acid wash on your pool walls and using a strong bristled brush will help remove their protective coating. Then, over a period of time, you carry out vigorous brushing to completely remove them from your walls. In some cases, you might only be able to reduce them, but not totally get rid of them.

However, after the mechanical scrubbing, you can now treat them with a combination of trichlor and copper-based algaecide. You first shock with the trichlor, and then, when the chlorine levels have returned to normal, you can treat with algaecide.

Even after eliminating black algae, care must be taken to prevent any lingering spores or remnants from your pool. Give your filter a proper backwash to prevent the re-entry of the black algae into your pool. 

  • Yellow/mustard algae: Yellow/mustard algae is usually the most difficult algae to deal with. This is because they are often misdiagnosed and yellow algae can still thrive in chemically balanced water. This is to say that they are basically chlorine resistant.

As to being misdiagnosed, yellow algae can be mistaken for green algae. This is because in a blue pool, yellow plus blue will appear to be green. However, one of the characteristics of green algae is that it makes the water hazy and murky.

Another thing it could be mistaken for are pollen grains. They have a similar color. However, a way to differentiate them is that if it’s pollen or dirt, when brushed, they don’t stick to the walls. Pollen drops easily to the bottom of the pool. But in the case of yellow algae, it keeps coming back.

To eradicate yellow/mustard algae, you will need to make use of a chlorine enhancer or an algaecide that is specifically designed to target the yellow algae. Sodium bromide is also known to be quite effective at dealing with mustard algae.

Why is chlorine not killing algae?

There are a number of reasons why your chlorine is not killing the algae in your pool. I will list some of these factors below:

  • High pH: Chlorine does not work well in water with a high pH. The recommended pH range for chlorine to sanitize effectively is between 7.2 and 7.8. In waters that have a higher pH than this, chlorine can lose up to 90% of its effectiveness. As a result of this, algae can grow unchecked. Though you might be shocking your pool and sanitizing it routinely, your pool will still remain cloudy with algae. In general, high pH encourages the growth of algae.
  • High phosphate levels: Phosphate can enter into your pool from detergents and runoff from fertilizers. Phosphates are basically food for algae. This means that though you might be sanitizing your pool, if the phosphate levels are high, the algae will keep being fueled. They continue to bloom because they are getting nutrients. It is essential to reduce your phosphate levels so the algae are starved, and then your chlorine works more effectively.
  • Chlorine lock: Chlorine lock is a situation whereby, despite adding more chlorine, the chlorine in your pool is still rendered useless. This situation can come about when there is excess cyanuric acid in your pool. Cyanuric acid is what forms pool stabilizers that you use to extend the lifespan of chlorine in your pool. However, this stabilizer can have drawbacks when used in excess.

Naturally, cyanuric acid reduces the sanitizing ability of chlorine. If it gets to excess, it can totally render the oxidizing power of chlorine null. As a result, you must ensure you properly check and adjust the levels of sanitizer in your pool. The ideal range is between 80 and 120 parts per million. If it is above that, you must ensure you partially drain the pool and dilute it.

How much chlorine will kill algae?

If you are experiencing an algae outbreak, you have to increase your chlorine concentration to a breakpoint of over 30 parts per million. The severity of the algae infestation will also determine how much shock you will use. For light green pools, you can administer 1 pound of shock for every 10,000 gallons of water. For a very dark green pool, you might have to use up to 3 pounds of shock per 10,000 gallons of water.

How long does it take for chlorine to kill algae?

This depends on the severity of the algae manifestation. Chlorine can take 1-3 days to eradicate algae. Sometimes, it could take up to a week if it’s very severe.

Should I use shock or algaecide first?

Shock should always be used first. The reason for this is that chlorine can destabilize the chemical bonds in the algaecide. It is advisable that after shocking your pool, you wait till the levels of chlorine have come down to normal( 1 to 3 parts per million) before applying algaecide. This will help your pool to have a healthy dose of algae prevention.

Why is my pool still green after shock and algaecide?

If your pool is still green after adding shock and algaecides, it could be as a result of chemical imbalances in your pool: These imbalances could include: high pH, high alkalinity, or chlorine lock.

What naturally kills algae?

Vinegar and baking soda are some natural alternatives that you can use for algae treatment. When trying to deal with black algae, baking soda can help loosen those deep roots. Applying it to those stubborn spots and brushing them down can be quite effective.

Vinegar is also another option that is quite effective. Apply it to those problem areas and scrub down.

Will sunlight kill algae?

No, it won’t. In fact, on the other hand, sunlight will act as an aid to their growth. Most green algae contain chlorophyll, and they have the ability to carry out photosynthesis. This means that, in the presence of sunlight, they will be able to make their own food and nutrients to thrive.

Can I vacuum algae out of my pool?

Yes, you can. Vacuuming your pool can help you get rid of suspended algae. However, you must ensure that you treat your pool chemically to kill the algae first. Some algae will stick tightly to your walls, and your vacuum might not be able to remove them.

At what temperature does algae grow in a pool?

Algae likes to bloom in warmer temperatures. Temperatures of 85°F and above are very conducive to the growth of algae.

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