You already know you need chlorine in your pool to keep the water clean and clear.
But how often should you top up your pool with fresh chlorine, and does it really matter how often you add it to your water?
Quick answer: On average, slow-dissolving chlorine tablets can last a week or longer between top-ups, while those who manually add liquid or granular chlorine to their water will have to do this every day or at least every other day.
Why Chlorine Top-Up Frequency Matters
The ideal chlorine level in a pool is typically between 1-3 parts per million (ppm).
For most pools, having this amount of chlorine in the water provides enough sanitizing power to deal with everyday contamination without causing too much discomfort to anyone using the pool.
But chlorine doesn’t last forever.
From the moment you add chlorine to your pool, it immediately starts getting used up in the sanitation process. As a result, your ideal 3 ppm reading could end up dropping below 1 ppm by the following day.
A gradual loss of free chlorine is normal and expected in any pool, but it should never be allowed to drop to a point where it’s unable to effectively sanitize your water (e.g. below 1 ppm).
Knowing how often to add chlorine, even just generally, will prevent your chlorine level from falling below the minimum effective level — especially when you don’t always have time to test your water beforehand.
So How Often Should You Add Chlorine?
Every pool is different, which means there’s no universal answer for how often you need to add chlorine to your pool water.
It all depends on the rate of chlorine consumption in your pool, and this is influenced by things like:
- What type of chlorine you’re using
- The delivery method for that type of chlorine
- How much direct sunlight your pool is exposed to
- How many people use your pool throughout the day
- What contaminants enter your water throughout the day
- The weather conditions on a particular day
- The average temperature of your water
- Whether your pool is indoors or outdoors
- And so on…
So where do you go from here?
In order to figure out how often to add chlorine to your water, you first need to figure out how much chlorine you’re losing over time (otherwise known as your chlorine consumption rate).
So let’s do that next.
How to Determine Your Chlorine Consumption Rate
The only way to know how much chlorine your swimming pool is consuming is to test your water.
Here’s the exact process to follow:
- Test your free available chlorine (FAC) level using a liquid testing kit or pool test strip.
- If it’s below 1 ppm, you don’t have enough chlorine in your water for this process. Add more chlorine, wait an hour, then start again from step 1.
- Make a note of your free available chlorine level. Write it exactly as shown.
- Wait 24 hours. Be sure to let the pool run under normal conditions during this time, as this will give the most accurate results.
- Test your FAC level again using the same testing method.
- Calculate the difference between both readings by subtracting the first number from the second number.
- The resulting number is your daily chlorine consumption rate.
For example: If your first FAC reading is 3.5 ppm, and 24 hours later you get a reading of 1 ppm, your daily consumption rate is 2.5 ppm.
Once you know how much chlorine your water consumes on a daily basis, you’ll know exactly how much chlorine you need to put back in.
With that said, your daily chlorine consumption rate is still only ever a semi-reliable estimate as daily conditions will never be identical. This is why regular testing will always be a staple of your pool maintenance process.
What Can You Expect in Terms of Frequency?
We will do our best to give you a general estimate of how often you should be adding chlorine to your pool.
This will be based on the type of chlorine you’re using as it’s the single biggest variable when it comes to answering this question.
Important: These are rough estimates and should not be used in place of calculating your chlorine consumption rate. This is only intended to give you an idea of what to expect.
Chlorine Tablets: Every 5-7 Days
Chlorine tablets are typically either placed into a floating dispenser, skimmer basket, or chlorine feeder.
This slow-release form of chlorine will often last up to a week under normal conditions. However, warmer temperatures and high pool usage will cause tablets to break down much faster than that.
Chlorine Granules: Every 2-3 Days
Granular chlorine is usually measured out and pre-mixed in a bucket before being added to the water.
Once added to the water, this type of chlorine will raise your chlorine level much faster than chlorine tablets as it’s already broken up and (mostly) dissolved. It will also be consumed noticeably quicker at around 2-3 days.
Liquid Chlorine: Every 1-2 Days
Liquid chlorine (sodium hypochlorite) usually comes in 1-gallon jugs and can be poured directly into the water, though using a measuring cup is often preferred.
This form of chlorine gets to work almost immediately once added to your water, making it the fastest-acting form of chlorine you can use in a pool. It also needs to be topped up on a near-daily basis.
Saltwater Generator: Only When Needed
Saltwater pool systems are designed to introduce chlorine into the pool automatically, on an ongoing basis. This chlorine level is set and maintained by the salt system interface.
In general, you shouldn’t need to add any additional sources of chlorine to a saltwater pool, but there are exceptions to the rule — such as exceptionally high bather loads, extreme weather conditions, or algae growth.
What Should You Do When Taking a Vacation?
Unless you have a saltwater generator, topping up your chlorine is going to be a pretty regular manual task.
So how do you prepare your pool when you’re away?
Well, the best option is always to have someone else do it on your behalf.
Knowing your chlorine consumption rate will negate the need for testing (at least temporarily), which makes the job much easier. On top of that, using liquid chlorine (again, at least temporarily) will make it almost idiot-proof.
If asking someone to fill in isn’t going to work, the next best approach is to use tablets or pucks for a slow and steady release of chlorine.
This approach should buy you around a week of downtime before the chlorine level starts to diminish. It does, however, add cyanuric acid and calcium to the water, so you’ll want to monitor that if you’re not already using tablets.
Finally, for slightly longer trips, consider raising your chlorine to shock level before adding tablets, as this will give you a bigger buffer.
The Bottom Line
The only way to truly know how often to add chlorine to your pool is to learn your chlorine consumption rate through regular testing.
Without this number, you’ll need to rely on third-party estimates that could leave your water deficient in sanitizer and vulnerable to contaminants like algae, and this can be difficult to correct later on.