Chlorine tablets or pucks offer a low-effort way to keep your water clean.
But exactly how long do chlorine tablets last? Does it matter how you add them to your water? And how often should you refill them?
Quick answer: Most tablets last between 5-7 days before dissolving completely, though smaller tablets in warmer water can dissolve in as little as two days. Using an automatic chlorinator will more than double this timeframe.
Your Pool Conditions Matter (A Lot)
The conditions of your pool create a ton of variability around how fast tablets dissolve, taking the duration anywhere from a day to several weeks.
For example, you have to account for:
- Delivery method. How your tablets are added to your pool, be it through a floater, skimmer basket, or feeder. This is the single biggest factor.
- Delivery settings. Floaters have adjustable vents, skimmer flow is controlled by the pool pump, and a feeder has settings to regulate flow.
- Tablet size. 3-inch tablets dissolve slower than 1-inch tablets. Different shapes with more/less surface area will also impact the dissolution rate.
- Tablet type. Trichlor-based chlorine tablets (the most popular) typically dissolve slower than dichlor or calcium hypochlorite tablets.
- Water temperature. Warmer water dissolves chlorine tablets considerably faster than cooler water.
- Water flow. The more water flow or movement around the tablets, the more turbulence they experience and the faster they dissolve.
- Tablet age. Stored improperly, older chlorine tablets may dissolve slightly faster or slower than brand-new tablets.
- Tablet quantity. Whether you’re stacking several tablets on top of each other, or letting a single tablet do the work.
- Sun exposure. Direct sunlight weakens the chemical bonds in chlorine tablets which make them break down faster.
Fun fact: The rate your chlorine tablets dissolve has nothing to do with how large your swimming pool is. The volume of water in your pool only dictates how many tablets you need to add at one time.
How Long Do Chlorine Tablets Last? (For Each Delivery System)
Despite all the variables above, we’ll try our best to answer the question for each chlorine delivery system.
We’re going to assume you’re using 3-inch trichlor tablets under moderate conditions, as this is the likely scenario for most pool owners.
However, you can still use our averages under slightly different conditions. If you’re using smaller tablets and your pool tends to be warmer, take the low end of our range as a maximum duration. If your pool is cooler and doesn’t get much use, take the lower end of our range as a minimum duration.
Note: Remember, this is how long the tablets physically take to dissolve, not necessarily how long the chlorine being introduced to your water lasts.
Let’s get into it:
Floating Dispenser: 5-7 Days on Average
On average, chlorine tablets fully dissolve between 5 and 7 days inside a floating dispenser.
When tablets are used in a chlorine floater or dispenser, the release of chlorine is steady as the water slowly passes through the vents.
While a floater does expose the tablets to water at a constant rate, they typically aren’t exposed to heavy movement or turbulence in the water which often speeds up the dissolution rate.
Floaters can also get stuck on stairs or behind ladders, significantly reducing the water flow and ultimately the dissolution rate. However, it’s best to avoid this as it can create a buildup of acid that will damage your pool surfaces.
Skimmer Basket: 3-5 Days on Average
On average, chlorine tablets last between 3 and 5 days inside a skimmer basket.
When tablets are used in a skimmer basket, chlorine enters the pool when water passes through the pool’s circulation system. This happens at a fairly steady rate but it’s not as consistent as using a floater because the pump isn’t always running.
On the same note, when the pump is running, the tablets are subjected to a much higher flow of water compared to being in a floating dispenser, and this is primarily why the tablets dissolve a little faster.
Automatic Chlorinator: 7-10 Days on Average
On average, chlorine tablets last between 7 and 10 days inside an automatic chlorine feeder.
When tablets are used in an automatic chlorinator, the release of chlorine is controlled as it runs through a chamber operated by a valve or flow meter. This allows for the precise administering of chlorine into the pool.
Doing it this way also minimizes the amount of water flow and turbulence because it shuts off circulation until chlorine is actually needed. Since there’s less movement inside the chamber, the dissolution rate is reduced.
Overall, this is widely considered the best way to use chlorine tablets in a pool, both for creating a slow and controlled release of chlorine and for the benefit of being even more hands-off than using a floater.
How Often Should You Top Up?
This might seem obvious, but you should never let your tablets completely dissolve before adding more tablets.
Doing so, even if only for a short time, will allow your chlorine level to drop just enough for algae to potentially take hold. Once this happens, you’ll need even more chlorine to get back to where you started.
For this reason, you’ll want to refill your floater, skimmer basket, or chlorine feeder when most of the tablets have been dissolved, but not completely. The averages above should be considered a deadline rather than a goal.
For example, instead of waiting 5-7 days before refilling a floating dispenser, it’s best to check the dispenser on day 4 and be ready to top up if most of the tablets have already been dissolved.
The Bottom Line
For most pool owners, topping up a floating dispenser or refilling your skimmer basket will become a once-weekly task, or as often as twice-weekly under more demanding conditions.
If you’re fortunate enough to have an automatic chlorinator installed, you may only need to refill the chamber every two weeks, and possibly even less frequently under less demanding conditions.
Either way, as long as you never let your tablets completely dissolve away, you should be able to maintain a steady chlorine level regardless of which delivery system you happen to be using.