Free Chlorine Lock-What is High vs Total & Combined Chlorine, Why Does it Disappear (2021)

There is no limit to the problems you can face with a swimming pool.

Each problem leads to a different level of damage to the pool.

Moreover, they have different solutions too.

It has been observed that if you do not follow the correct solution, then it can damage the pool further.

One of the most challenging problems is the chlorine lock.

Do not worry.

Whether you are hearing about it for the first time or you are facing it, in this blog, we will discuss it deeply.

We will also discuss some effective solutions to get break chlorine lock-in pool water.

What is free chlorine lock?

Free Chlorine in a Pool

Let us understand this by an example.

Shall we?

Assume that you fill the fuel tank of a vehicle.

However, the fuel does not reach the engine.

What will happen?

Yes, the engine will not start.

This is also known as fuel lock, in mechanical terms.

Similarly, when you add chlorine to the pool, and it does not sanitize the pool, it is known as chlorine lock.

You can also say that the chlorine does not react in the water.

This situation is common among pool owners who have had a pool for years.

Is there a solution?

Yes, there are some effective solutions to this problem.

Why does the chlorine in my pool disappear?

There are two reasons for it.

The first reason is an imbalance in the PH of the pool water.

Maybe it is too acidic or too basic.

Irrespective of it, you must make sure that it remains balanced.

It can even happen due to an increase in the amount of cyanuric acid.


Well, this acid is itself a sanitizer.

Thus, by adding it, the effect of chlorine gets neutralized.

Techniques/Tips to Improve Free Chlorine in a Pool

Water chemistry (keep free chlorine high enough)

The first method to deal with the problem is to maintain the water chemistry.

Usually, most of the problems in the pool happen due to an imbalance in chlorine levels.

Thus, you should try to balance the chlorine level as soon as possible.

What you must check and how to check them all?

Well, the best way to check the water chemistry of the pool is to use a pool test kit.

Make sure that you choose one of the top brands of test kits.

The pool kit should be accurate and within your budget.

Now, you will be able to check the water chemistry and free chlorine level of the pool.

You will surely get accurate results.

These results will include PH, salt, stabilizer level, chlorine, and many more.

You have to check whether any of them are in an inappropriate amount.

If there is one, then you must deal with it immediately.

Make sure that the overall water chemistry remains balanced.

What will you have to use to balance it?

Well, various chemicals in the market can be used to balance the pool chemistry.

In the case of chlorine, there are shock products including non-chlorine shock.

Similarly, you will find a chemical balancer for each element in the water.

Draining until free chlorine is high enough

Alright, so the present condition of the pool does not let the chlorine react.

Another way to deal with this situation is by draining.

Yes, you can do complete draining and re-fill the pool.

However, that method can be a little costly.

Thus, you can try to drain out half of the pool.

Now, re-fill the pool and use the pool test strips again.

How will it remove chlorine lock?

As mentioned earlier, this issue usually happens due to the increase in the level of the acid.

Thus, if you can reduce the level of acid, then the problem will be solved.

By partially draining the pool, and re-filling it, we are decreasing the concentration of acid.

Correcting free chlorine common problems

How to deal with chlorine lock?

As mentioned earlier, the acid is one of the main reasons behind the chlorine lock.

Therefore, an obvious solution may come to your mind: remove it from the pool.

However, this will not help you get rid of the problem.

Let us understand the reason.

Chlorine usually becomes ineffective due to the presence of sunlight.

Therefore, if you add it in the middle of the day, then it is likely that it will be ineffective.

The use of the acid comes in here.

The acid works as sunscreen lotion or sun protection for chlorine.

Thus, having cyanuric acid in the pool is necessary.

However, the excess amount of this acid leads to the chlorine lock.

In conclusion, you must not eliminate the acid from the pool.

Let us say that you do that, then the chlorine in the pool will remain ineffective.

Therefore, you must always add this acid in the pool.

What is chlorine demand? Is it the same as chlorine lock?

You will observe most of the companies in the market using the terms interchangeably.

However, they are not the same.

There is a huge difference between both of them.

In simple terms, chlorine demand is a situation, where the pool lacks chlorine.

Thus, it demands you to add more.

On the other hand, chlorine lock is a condition, where the chlorine in the pool does not react or treat the water.

It remains ineffective.

Both issues also have different solutions.

Frequently Asked Questions About Free Chlorine

How do you fix chlorine lock?

Let us recap.

The first method is to balance the water chemistry in the pool.

This is how to break chlorine lock-in pool water by eliminating any imbalance of elements in the pool.

Thus, through a pool test kit, you must identify the main reason behind an imbalance in water chemistry.

As per the results, you must add chemicals to balance the pool chemistry.

The second method is to partially drain the pool and re-fill it.

The main objective of this method is to decrease the concentration of cyanuric acid in the pool.

You can even completely drain the pool to get rid of the problem.

Just make sure that after complete drainage, you clean the pool.

Why can’t I get a chlorine reading in my pool?

This is not normal if you use a reliable test kit.

Check the pool test kit is not out of date.

Try a different type of test, such as a digital tester.

Is it safe to swim in a pool with chlorine lock?

No, it is not safe.

Since it gives a chance to bacteria and algae to grow.

Swimming in the pool will lead to skin allergies and eye redness.

Thus, you must avoid swimming in the pool at any cost.

What is chlorine lock in a swimming pool?

It is a condition when the chlorine does not react with water.

Thus, the water does not get sanitized.

Moreover, this gives a perfect breeding ground to bacteria and algae.

Therefore, you must solve the problem as soon as possible.

What is the difference between free chlorine and total chlorine?

If we talk about free chlorine, then it is the amount of chlorine in the pool that has sanitized pollutants.

Whereas, total chlorine is the combination of free and combined chlorine.

What is combined chlorine?

Well, it is the amount of chlorine that can be in direct contact with pollutants.

Analysis of best practices in the industry

  • Maintain the water chemistry
  • Choose an accurate test kit
  • Use shockers
  • Clean the pool after complete draining

Tools you can use

  • Pool test kit
  • Pool chemicals
  • Drainage system