Why doesn’t a car have a battery meter to tell us when to replace it instead of finding out it’s flat when we try to start it? Turns out car batteries aren’t as simple to measure as a fuel gauge, that’s why. With a salt water pool, you might assume that modern technology measures chlorine in the water, right? That’s assuming you’re even aware that salt water pools do contain chlorine!
Most modern salt water pool chlorinators measure live salt readings but don’t include live chlorine readings as a standard feature. While it can be bought as a separate add on, it’s a sophisticated feature that adds a significant cost to the chlorinator and isn’t included standard.
Why doesn’t a salt water pool measure chlorine?
Original salt water pool systems were very basic and only offered very limited functionality to measure various aspects of water chemistry. Regular chlorine pools by comparison didn’t offer any readings and everything had to be tested manually each week to keep water levels balanced. More expensive salt water pool chlorination systems offer live chlorine monitoring but at an extra cost rather than standard.
Hayward offers their Sense and Dispense module which is an add on to their AquaRite Pro chlorinator system. Sense and Dispense automatically monitors and balances chlorine and automatically senses both pH and oxidation-reduction potential (ORP) in the pool but it adds about $700 to the cost of the chlorinator.
Some cheaper chlorinator brands don’t even cost $700.
In case you’re new to salt water pools, they do contain chlorine. Many people hear salt water pool and they think this means there is no chlorine, but this is not the case.
Here’s the difference between a chlorine pool and a salt water pool:
- Regular chlorine pools that we grew up with use liquid or crystal chlorine that is dumped into the pool each week to keep it sanitized and clean. If you’ve ever swam in a pool of this kind, you know the strong chlorine smell that remains on your hair, skin and swim clothing. You may even experience red eyes if you open them underwater.
- A salt water pool uses a salt water chlorination system to convert salt to chlorine. It’s still chlorine but it’s a milder form and doesn’t come with the associated smell and it also tends to be easier on your hair, skin and swim clothing.
From time to time, you might be required to dump chemical chlorine into your salt water pool. Commonly you add chlorine to your salt water pool when opening it and again when closing it. You might also choose to shock the pool from time to time to quickly raise chlorine levels which we’ll talk about more below.
Do you test for chlorine in a salt water pool?
You need to test for chlorine in a salt water pool just like a regular pool. If your chlorinator system monitors it automatically such as Hayward’s AquaRite Pro with Sense and Dispense feature, then your chlorine and pH level is adjusted automatically for you.
Chlorine is measured in parts per million (ppm) and needs to be kept between 1ppm and 3 ppm at all times. If you check chlorine and it consistently runs too high, you might run your pump less or turn the chlorinator setting down slightly.
But when chlorine drops below 1, you run the risk of getting green water and algae developing. You need to keep your chlorine reading between 1 ppm and 3 ppm to avoid this. You may also hear 2 ppm – 4ppm as the suggested range so there is some debate. See what works for your pool, your pool usage and your local area ie. local weather conditions.
Using test strips to test chlorine each week is the quickest and easiest way to test and taking a water sample to your pool company every few weeks is a good back up plan.
How much chlorine does a salt chlorinator produce?
Depending on the size and rating of your chlorinator, an average chlorinator is capable of producing a maximum of 0.5 lbs – 1.5 lbs of chlorine per day. For larger pools, you can choose a chlorinator such as Hayward’s Saline C 6.0 chlorinator which produces up to 6 lbs per day for pools up to 125,000 gallons in size.
It’s typically recommended that you run your pool pump around 8 – 10 hours per day and set the chlorinator at 50% to start with and adjust it from there depending on your needs. The chlorinator can only produce chlorine when the pump is running and setting it at 50% means it’s actually producing chlorine 50% of the time that the pump is on, or about 4 hours per day in this case.
If you ran your pump 10 hours per day and had the chlorinator set at 40% you’d be producing chlorine for 10 hours * .6 = 6 hours per day.
So if you found that your chlorine reading is consistently low you might start by increasing pump time or you may increase the % that the chlorinator runs or you may do both together. Alternatively you would adjust settings downwards if chlorine production is too high.
Typically you adjust the % chlorinator run time to raise or lower chlorine levels slightly.
Do you still need to add chlorine in a salt water pool?
While a salt water pool produces chlorine through its chlorinator, there are times when regular chemical chlorine does get added.
Chlorine typically gets manually added to a salt water during certain occasions:
- Opening the pool in spring
- When the pool needs to be shocked due to various circumstances (keep reading…)
- Closing the pool for the winter
Let’s take a closer look at the issue of manually adding chlorine to your salt water pool as it probably seems counterintuitive to do so given that the purpose of a salt water pool is to avoid this.
How do I know if my salt water pool needs chlorine?
For a salt water pool to produce chlorine with salt, it needs some chlorine in the water already to assist in the process. So at certain times of the pool season, manually adding chemical chlorine is required.
In the spring when you are opening your pool, your chlorine level will undoubtedly be 0. Over the winter any chlorine left in the water from the autumn when you closed the pool is long since gone. You add a large amount of chlorine to shock the system – hence the name of the product called pool shock – to start up chlorine production.
During summer season there may be occasions when your pool needs a bit of help to bump up chlorine production quickly given hot sunny weather, large amounts of rain, heavy pool usage and other factors that kill chlorine. Manually adding chemical chlorine quickly accomplishes this to keep the water properly sanitized.
And when closing the pool in autumn, it’s a good idea to increase chlorine levels because as soon as you shut the pool down for the winter, chlorine production stops. If you experience some warm weather after pool closing, it can turn the water green with algae. Adding chlorine (and an algaecide) right before pool closing can help to prevent water contamination until the water temperature drops below 60 degrees for good.
When should I shock my salt water pool?
Shocking a pool refers to adding a concentrated amount of chlorine to quickly bump up chlorine levels to deal with a certain event(s) affecting the pool.
Other than opening and closing your pool, specific reasons to shock your pool include:
- Very hot sunny weather when temperatures suddenly spike higher
- Heavy pool usage, pool parties or when many kids are in the pool ie. increased contaminants from human use
- After your dog or other animals were swimming in the pool
- Heavy rainfall which dilutes chlorine in the water which also may result in you having to drain some water
- To reduce the onset of algae before it becomes a bigger problem
As to when you should actually shock your pool:
- Add shock to your pool after dusk when the sun has gone down
- Depending on the prevalence of the above incidents shocking a pool every 1 – 2 weeks is normal.
How should I shock my salt water pool?
There are two schools of thought on this subject depending on what you prefer. Using your chlorinator’s Super Chlorinate feature is one option and manually adding a chemical shock product is the other.
Before you choose one option over the other, it’s worth remembering that each chlorinator has a lifespan and is capable of producing a certain amount of chlorine before it dies and needs to be replaced at a cost of several hundred dollars or more depending on the model and pool capacity. Hayward salt cells typically cost $300 – $600 give or take.
So the more you shock the pool with your chlorinator the more you use its capacity up and the sooner you will have to replace it. Hayward calls its shock feature Super Chlorinate whereas you might hear Super Boost or some other phrase used.
Hayward tells you exactly what they expect their salt cells to produce before they need to be replaced:
Their T-CELL-3 can produce 210 lbs of chlorine (Trichlor) and their T-CELL-15LL can produce 710 lbs of chlorine during their lifetimes respectively.
So while some people will use their chlorinator to Super Chlorinate, others may prefer to use a chemical product.
How long should you super chlorinate a salt water pool?
It depends on how much extra chlorine you require. If you plan on using your Super Chlorinate feature, it’s often recommended by the manufacturer to run it for up to 24 hours.
When you run the Super Chlorinate feature, it overrides your current settings and tends to produce chlorine 100% of the time that the pump is running.
So while shocking a pool with liquid or crystal shock will raise the chlorine levels quickly, the Super Chlorinate feature of your chlorinator system will raise chlorine levels over a period of time typically up to 24 hours.
Why does my pool reading show no chlorine?
Even if your pool looks crystal clear, it’s possible you have no chlorine present. If you test your pool water and get a 0 chlorine reading, you are a short time away from starting to experience cloudy and eventually green water as your pool needs chlorine to remain sanitized.
Commonly, your pool may show no chlorine for the following reasons:
- Your test strips or other testing mechanism is wrong. If you’re using expired test strips, get new ones as some strip brands are notoriously inaccurate and more so when expired.
Assuming the testing is accurate and you actually have 0 chlorine, you might have one of the following problems:
- Your salt cell isn’t producing chlorine. Check your salt chlorinator system’s diagnostics to see if the check cell light is on and if the cell is actually functioning.
- Your salt cell is producing chlorine but isn’t producing enough. You might need to run your pump longer and/or turn the chlorinator’s setting up to produce more chlorine.
- Your salt cell is producing chlorine but the pool is not holding it ie. it’s unable to retain the chlorine. This is known as chlorine lock.
Why does my pool not hold chlorine?
Chlorine lock occurs when your stabilizer is too high. When CYA (stabilizer) runs too high, it overwhelms the chlorine and prevents it from doing its job and why your pool reads 0 chlorine. Your pool will quickly start to turn green.
Chlorine lock can also occur when your pH is unbalanced.
Test your pool water to understand what your current chlorine, pH, stabilizer and other readings are so you can figure out what to do.
This is why it is important to keep your pool water balanced at all times. When one reading goes out of range it can drag other ones out as well and suddenly you have a green pool to deal with.
How can I fix chlorine lock?
Once you have tested your water and have your current readings in hand, you can do the following:
- Drain some water from your pool and replace it with fresh water to reset the chemistry and start over to balance it. The amount of water to be drained depends on how high the stabilizer reading is OR
- Use a non-chlorine shock oxidizer product which will oxidize the chlorine and water in your pool to restore water balance.
If you’re unsure and feel like you’re guessing, consult your pool company with a water sample to find out what your current readings are and to get a path forward to fix it.
Free chlorine vs combined chlorine vs total chlorine
There are actually three kinds of chlorine in your salt water pool that you should become familiar with.
Free chlorine: This is chlorine in the pool at that moment that is free to sanitize contaminants in your pool. This is the one you want to become familiar with the most because if represents the available chlorine in your pool at any given time that can kill contaminants and keep the pool clean. This should be kept in the range of 1 ppm – 3 ppm at all times.
Combined chlorine: This is chlorine in the pool at that moment that has already combined with contaminants and has been used.
Total chlorine = Free chlorine + Combined chlorine added together.
Pool test strips come in a variety of types that are capable of testing a number of different aspects of pool chemistry. You will typically find test strips that test total chlorine and/or free chlorine.
Summary
Salt water chlorinator systems monitor various aspects of water chemistry depending on which model you choose. While a cheaper model may have basic functionality, you can choose models up to and including ones that monitor chlorine and help to balance pH too. These models however come at a cost and these features are not currently included standard on average or even higher end chlorinators and are generally considered an expensive paid add on.
Learn more about salt water chlorinators including how to choose one (factors to consider) and the benefits of a salt water pool over a regular chlorine one.