Chlorine tablets dissolve slowly in your pool water to kill bacteria and algae
Chlorine tablets are solid forms of chlorine that release the chemical gradually as they dissolve. You place them in a floater, skimmer basket, or chlorinator — a device that holds the tablet and lets water flow around it — and they work continuously to sanitize your pool. The slow release means you don't have to add chlorine every day the way you would with liquid chlorine or powder.
Most tablets are made of trichlor (which also lowers pH) or dichlor (which is pH-neutral). Trichlor is cheaper and more common for residential pools. Both types do the same job: kill pathogens and prevent cloudy water. The main difference is how they affect your pool's acid level, which you'll monitor separately.
The tablets work best when water temperature is above 60°F. In cooler water, they dissolve much more slowly, so you may need to adjust how many you use or switch to a different chlorine form in late fall or early spring.
Key Takeaways
- Chlorine tablets release sanitizer slowly over days or weeks, so you add them once and let them work rather than dosing daily.
- You need a floater, skimmer basket, or automatic chlorinator to hold the tablet — never drop it loose in the pool.
- Test your pool water at least twice a week and keep free chlorine between 2 and 4 parts per million (ppm) for safe swimming.
- Tablets dissolve faster in warm water and slower in cool water, so you may need to add more tablets or fewer depending on the season.
- Trichlor tablets lower pH while dichlor tablets do not, so know which type you have before adjusting your water chemistry.
Choose a delivery method: floater, skimmer, or chlorinator
A floater is the simplest option — a plastic container that bobs on the surface and holds one or two tablets. Water flows through holes in the floater, dissolving the tablet gradually. Floaters are cheap and work, but they can damage pool liners if they sit against the same spot too long, and they drift around rather than staying where you want them.
A skimmer basket sits inside your pool's skimmer (the intake box at the pool edge). You place a tablet there and the pump pulls water through it. This keeps the tablet out of sight and prevents liner damage, but it only works if your pump is running. If you turn the pump off for hours, chlorine stops being added.
An automatic chlorinator (also called a feeder or erosion feeder) attaches to your pool's plumbing and holds multiple tablets. Water flows through it at a controlled rate, so you can adjust how fast the tablets dissolve. These are the most reliable but also the most expensive option and require basic plumbing knowledge to install. Many people hire a pool professional for this.
For most residential pools, a floater or skimmer basket is enough. Pick floater if your pump runs only part-time; pick skimmer if your pump runs most of the day.
Add tablets and monitor the water level in your floater or feeder
Start with one tablet per 10,000 gallons of pool water per week, though this varies based on water temperature, sunlight, and how much the pool is used. If you don't know your pool's volume, measure the length, width, and average depth in feet, multiply them together, then multiply by 7.5 to get gallons. A typical residential pool is 15,000 to 20,000 gallons.
Drop the tablet into your floater, skimmer basket, or chlorinator. If you're using a floater, close it and let it drift. If you're using a skimmer, make sure the basket sits properly so water flows through it. If you're using a chlorinator, follow the manufacturer's instructions for the flow rate.
Check the tablet every few days. As it dissolves, you'll see it get smaller. When it's nearly gone, add a new one. Don't wait until it disappears completely — add the next tablet when the current one is about the size of a quarter. This keeps chlorine levels steady.
In summer or when the pool gets heavy use, tablets dissolve faster and you may need to add them more often. In cooler months, they last longer.
Test your pool water twice a week and adjust tablet count
Buy a test kit (a kit with color-matching vials, usually $15 to $30) or test strips (cheaper, less precise, but faster). Test for free chlorine, total chlorine, pH, and alkalinity. Free chlorine should stay between 2 and 4 ppm for safe swimming. Total chlorine should be close to free chlorine; if it's much higher, you have chloramines (used-up chlorine) and need to shock the pool.
If free chlorine is below 2 ppm, add another tablet or move your floater to a sunnier spot (sunlight breaks down chlorine, so more sun means faster tablet use). If it's above 4 ppm, remove a tablet or slow the chlorinator's flow rate.
pH should be between 7.2 and 7.6. If you're using trichlor tablets, pH will drift lower over time — you'll need to add pH increaser (sodium carbonate) every week or two. If you're using dichlor, pH stays more stable. Alkalinity should be between 80 and 120 ppm.
Test more often in summer or after heavy rain, which dilutes chlorine and changes pH.
Handle tablets safely and store them correctly
Chlorine tablets are corrosive and can burn skin or eyes. Wear gloves when handling them and avoid breathing dust from a crumbling tablet. 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 care.
Never mix chlorine tablets with other pool chemicals — especially not with acid, algaecide, or shock. The combination can create toxic gas or start a fire. Store tablets in a cool, dry place away from other chemicals, away from children and pets, and away from direct sunlight. A plastic bin in a garage or shed works well. Keep the original container or a sealed plastic bucket; don't leave tablets loose.
If a tablet falls on the deck or ground, pick it up with a stick or tongs (not your hands), rinse the area with water, and put the tablet back in storage. Don't leave it sitting where someone could step on it.
Know when to switch to a different chlorine form
Tablets work best when your pool temperature stays above 60°F and you can test water at least twice a week. If your pool closes for winter or if water temperature drops below 50°F for weeks at a time, tablets dissolve so slowly that you can't control chlorine levels. Switch to liquid chlorine or powder chlorine for that period, then go back to tablets when water warms up.
If your pool has a lot of algae or the water is very cloudy, tablets alone won't fix it fast enough. You'll need to shock the pool first (add a large dose of chlorine all at once) and then use tablets for maintenance. Shock comes as powder or liquid; follow the product instructions.
If you travel and can't test water for a week or more, tablets are actually ideal because they keep working without you. But if you're home and can test regularly, tablets give you the most control and the least work.
Frequently Asked Questions
Can I put a chlorine tablet directly in the pool without a floater or skimmer?
No. A loose tablet will sink and sit on the pool floor, dissolving unevenly and potentially damaging the liner or concrete. It can also create a dead spot with no chlorine circulation. Always use a floater, skimmer basket, or chlorinator to hold the tablet where water can flow around it evenly.
How long does one chlorine tablet last?
A standard 3-inch tablet lasts 3 to 7 days depending on water temperature, sunlight, pool size, and how much the pool is used. Warmer water and more sun mean faster dissolution. Check every few days and add a new tablet when the current one is about the size of a quarter.
What's the difference between trichlor and dichlor tablets?
Trichlor tablets lower pH as they dissolve, so you'll need to add pH increaser regularly. Dichlor tablets are pH-neutral and don't affect your acid level. Trichlor is cheaper and more common. Dichlor is better if you want to avoid constant pH adjustments, but it costs more.
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 fast and makes chlorine levels hard to control. Hot tubs usually use liquid chlorine or powder chlorine instead. Check your hot tub manual for the correct chlorine form.
What should I do if my pool turns green after I add tablets?
Green water means algae is growing faster than tablets can kill it. Test your chlorine level first — if it's below 2 ppm, add another tablet when ready. If chlorine is at the right level but water is still green, you have an algae bloom and need to shock the pool with a large dose of chlorine. Tablets alone won't catch up. After shocking, resume normal tablet maintenance.