Drop tablets into a chlorine floater or feeder, and let them dissolve slowly over several days
Pool chlorine tablets (also called trichlor or dichlor tablets) work by releasing chlorine into your water as they dissolve. You do not drop them directly into the pool. Instead, you place them in a floating dispenser or an in-line feeder that holds them above or beside the water, letting the current and circulation carry the chlorine throughout the pool. A single tablet typically lasts three to seven days depending on water temperature, sunlight, and how much the pool is used.
The tablet slowly breaks down as water passes through or around it. This steady release keeps chlorine levels consistent without the shock of dumping powder all at once. Most pools need one tablet per week during normal use, though heavy use or hot weather may require more frequent replacement.
Key Takeaways
- Chlorine tablets must go into a floater or feeder, never loose in the pool, because they are too strong and can damage the pool surface and equipment.
- A floating dispenser is the simplest option for above-ground pools; in-line feeders work better for in-ground pools with circulation systems.
- Check and refill your dispenser every three to seven days, depending on how fast the tablet dissolves in your water conditions.
- Test your chlorine level twice a week with test strips or a kit to make sure it stays between 1 and 3 parts per million (ppm).
- Keep tablets in a cool, dry place away from sunlight, and never mix them with other pool chemicals or store them near acids.
Floating dispensers for above-ground and small pools
A floating chlorine dispenser is a plastic basket or cage that bobs on the water surface. You load one or two tablets inside, close the lid, and set it in the pool. As water splashes through the basket, it dissolves the tablet slowly. These cost between $10 and $30 and work well for pools under 15,000 gallons.
The dispenser has an adjustable opening or valve that controls how fast water reaches the tablet. If your chlorine level is dropping too slowly, open the valve wider. If it is dropping too fast, close it slightly. Check the dispenser every two to three days and refill it when the tablet is mostly gone. Empty dispensers can sink or get damaged, so do not leave one in the pool without a tablet.
Floating dispensers work best when your pool has good circulation — place it in the path of water returning from your pump or filter. If it sits in a dead spot, chlorine will not spread evenly and some areas may stay cloudy.
In-line feeders for in-ground pools with pumps
An in-line chlorine feeder attaches to the return line of your pump and filter system. Water is forced through a chamber holding the tablets, dissolving them under pressure. These feeders cost $50 to $150 and give you more control over chlorine release because you can adjust the flow rate.
To install one, turn off your pump, cut into the return line (the pipe carrying water back to the pool after filtering), and connect the feeder between the two cut ends using PVC fittings. Load tablets into the chamber, close it, and turn the pump back on. The feeder will dissolve tablets faster than a floater because the water pressure is stronger.
In-line feeders let you dial in exactly how much chlorine enters the pool each day. They also keep tablets out of sight and prevent them from getting knocked around by swimmers. The trade-off is that you need basic plumbing skills or a pool technician to install one, and you must turn off the pump to refill the chamber.
How often to check and refill your dispenser
Check your chlorine dispenser every two to three days during the swimming season. Look at how much of the tablet remains. If it is less than half gone after a week, your water is cool or your circulation is poor — you may need to add a second tablet or open the dispenser valve wider. If it is almost gone after three days, your water is warm or heavily used — you may need to close the valve or switch to a smaller tablet size.
When a tablet is mostly dissolved, remove the dispenser from the pool, empty any remaining pieces, rinse it with pool water (not tap water), and load a fresh tablet. Do this in the evening so the new tablet has time to start working before you test the water the next morning. Never leave an empty dispenser in the pool for more than a few hours.
In very hot weather or during heavy pool use (parties, swim lessons), you may need to refill every three to four days instead of seven. Keep extra tablets on hand so you do not run out.
Testing chlorine levels to know if your tablets are working
Use a chlorine test kit or test strips to check your chlorine level twice a week. Test strips cost $10 to $20 for a bottle of 50 and give you a result in seconds — dip one in the pool, wait a few seconds, and match the color to the chart on the bottle. A liquid test kit costs $20 to $40 and is more accurate but takes a few minutes.
Your chlorine level should stay between 1 and 3 parts per million (ppm). If it is below 1 ppm, your tablets are dissolving too slowly — open the dispenser valve, add a second tablet, or check that water is circulating properly. If it is above 3 ppm, close the valve or remove a tablet. If it is at zero, your tablets have completely dissolved and you need to refill when ready.
Test in the morning before anyone swims, because sunlight and swimmer activity both lower chlorine during the day. If your level drops more than 1 ppm in a single day, you may have a heavy algae bloom or a lot of debris in the water — shock the pool with a larger dose of chlorine powder and clean the filter.
Storage and safety for chlorine tablets
Store chlorine tablets in their original container in a cool, dry place away from direct sunlight. A garage, shed, or basement works well. Keep them away from heat sources, moisture, and other pool chemicals — especially acids, which can cause a dangerous reaction. Never store tablets in a metal container or near metal tools, because chlorine corrodes metal.
Tablets are strong oxidizers and can burn skin or eyes if handled carelessly. Wear gloves when loading them into a dispenser, and wash your hands afterward. If a tablet touches your skin, rinse when ready with water. If it gets in your eyes, rinse for at least 15 minutes and call poison control or seek medical attention.
Keep tablets out of reach of children and pets. A single tablet can cause serious harm if swallowed. Store them in a locked cabinet if you have young children in the house.
When to use shock treatment instead of tablets alone
Chlorine tablets keep your pool safe during normal use, but they cannot handle sudden problems like algae blooms, cloudy water, or a spike in bacteria. When that happens, you need shock treatment — a large dose of chlorine powder or liquid that you add all at once to kill contaminants quickly.
Shock your pool if your chlorine level stays at zero even after refilling your dispenser, if the water turns green or cloudy, or if you notice a strong chlorine smell (which means chlorine is being used up fighting contaminants). Follow the shock product's instructions for how much to add based on your pool size. After shocking, wait at least 24 hours before swimming and retest the chlorine level.
You can use tablets and shock together — shock handles the emergency, and tablets keep the level steady afterward. Many pool owners shock once a week in summer as routine maintenance, then rely on tablets the rest of the time.
Frequently Asked Questions
Can I put chlorine tablets directly in the pool?
No. Tablets are too concentrated and will damage the pool surface, vinyl liners, and equipment if they sit on the bottom or dissolve unevenly. They must go in a floater or feeder that controls how fast they dissolve.
How long does one chlorine tablet last?
Most tablets last three to seven days depending on water temperature, sunlight, and pool use. Warm water and heavy use speed up dissolution. Check your dispenser every two to three days and refill when the tablet is mostly gone.
What is the difference between trichlor and dichlor tablets?
Trichlor tablets are stronger and last longer, making them better for weekly maintenance. Dichlor tablets dissolve faster and are often used for shock treatment. Most floating dispensers use trichlor. Check your product label to see which type you have.
Why is my chlorine level dropping too fast?
Fast drop usually means warm water, heavy pool use, or strong sunlight. You may also have algae or debris consuming chlorine. Open your dispenser valve slightly less, add a second tablet, or shock the pool if the water looks cloudy or discolored.
Can I use chlorine tablets in a hot tub or spa?
Tablets are not recommended for hot tubs because the high temperature causes them to dissolve too quickly and can damage the tub's jets and heater. Use chlorine powder or liquid designed for hot tubs instead, and follow the manufacturer's dosing instructions.