Chlorine tablet calculator: how many tablets per week?
Tablets (trichlor) are 90% chlorine and about half stabilizer by weight. Enter your pool size and how much chlorine it uses a day to see the tablets per week — and where your CYA ends up.
Enter your measurements
More options: CYA · Weeks
- Chlorine one tablet adds
- 5.4 ppm
- Stabilizer (CYA) added per week
- 8.5 ppm
- CYA at the end of that time
- 132 ppm
- Tablets over that time
- 32 tablets
- Weight of tablets over that time
- 15.6 lb
In short: how much chlorine one tablet adds to your pool, how much the pool uses in a week, and the stabilizer the tablets leave behind.
One 8 oz tablet × 90% = 204 g of chlorine ÷ 37,854 L = 5.4 ppm
2 ppm a day × 7 = 14 ppm a week ÷ 5.4 ppm = 2.6 tablets
CYA: 14 ppm × 0.61 = 8.5 ppm a week; 30 + 8.5 × 12 weeks = 132 ppm
- At this rate CYA reaches about 132 ppm — above the 90 ppm the Model Aquatic Health Code allows in public pools, and high enough that chlorine has to run very high to stay effective. Many owners switch to liquid chlorine once CYA is in range, or plan a partial drain.
- Tablets supply chlorine slowly; they can’t raise chlorine quickly. For a fast rise or a shock, use liquid chlorine or cal-hypo — never in the same feeder or bucket as tablets.
- Trichlor is acidic, so pools on tablets tend to drift down in pH and alkalinity. Check both weekly.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How many chlorine tablets for a 10,000 gallon pool | 2.6 tablets |
| How many chlorine tablets for a 20,000 gallon pool | 5.2 tablets |
Tablets per week by daily chlorine use
| Use per day | Tablets per week | Stabilizer (CYA) added per week | CYA at the end of that time |
|---|---|---|---|
| 1 ppm | 1.3 tablets | 4.2 ppm | 81 ppm |
| 1.5 ppm | 1.9 tablets | 6.4 ppm | 106 ppm |
| 2 ppm | 2.6 tablets | 8.5 ppm | 132 ppm |
| 3 ppm | 3.9 tablets | 12.7 ppm | 183 ppm |
| 4 ppm | 5.2 tablets | 17 ppm | 234 ppm |
Three-inch tablets are trichlor: about 90% available chlorine, with the rest mostly cyanuric acid. That makes them convenient — drop a few in a floater and forget them — but every tablet that dissolves leaves stabilizer behind, and stabilizer never leaves except with water.
How the tablet math works
chlorine per tablet (ppm) = tablet weight (g) × 0.90 ÷ pool litres × 1,000 tablets per week = daily use (ppm) × 7 ÷ chlorine per tablet CYA added per week = daily use × 7 × 0.61
A 7 oz tablet in 10,000 gallons adds 4.7 ppm of chlorine — the figure printed on an EPA-registered trichlor label — and an 8 oz tablet about 5.4 ppm. The pool industry’s PHTA water-quality committee puts the stabilizer at 0.6 ppm of CYA for every ppm of chlorine trichlor adds.
What the labels say
Tablet labels give a weekly rate per volume, and they don’t agree with each other: one EPA label says 1 tablet per 8,000 gallons every 7–14 days; one retailer lists both one tablet per 10,000 gallons a week and one per 5,000 gallons replaced every 5–7 days. Those rates work out to roughly 0.5 to 1.5 ppm of chlorine a day — fine for a covered or shaded pool, short for a sunny, busy one. That is why this calculator starts from what your pool actually uses.
| Pool | 1 ppm/day | 2 ppm/day | 3 ppm/day |
|---|---|---|---|
| 5,000 gal | 0.6 | 1.3 | 1.9 |
| 10,000 gal | 1.3 | 2.6 | 3.9 |
| 15,000 gal | 1.9 | 3.9 | 5.8 |
| 20,000 gal | 2.6 | 5.2 | 7.8 |
| 25,000 gal | 3.2 | 6.5 | 9.7 |
Worked pages for the two most-asked sizes: how many chlorine tablets for a 10,000 gallon pool and how many chlorine tablets for a 20,000 gallon pool.
The stabilizer problem
At 2 ppm a day, tablets add about 8.5 ppm of CYA a week. A pool that opens at 30 ppm passes 90 ppm in about seven weeks. As CYA rises, the chlorine level needed to keep algae away rises with it (see the chlorine and stabilizer calculator), so a tablet-only pool often turns cloudy or green in late summer even though the floater is full. The usual fixes are to use tablets only until CYA reaches your target and then switch to liquid chlorine or a salt cell, or to plan a partial drain and refill.
Using tablets safely
- Put tablets in a floater or a feeder plumbed after the heater — never in the skimmer basket, where concentrated, acidic water flows through the pump and heater.
- Never put any other chlorine (especially cal-hypo) in a tablet feeder or bucket. The CDC warns not to mix different types of chlorine.
- Don’t let a floater park against vinyl steps or a liner; the concentrated water can bleach it.
- Store buckets closed, dry and away from acid and other chlorine.
What you’ll need
- 3-inch trichlor tabletsMid-range price
Slow-dissolving stabilized chlorine for a floater or feeder. Convenient, but every tablet adds stabilizer (CYA) and lowers pH.
See options on Amazon (opens in a new tab) - Floating chlorine dispenserBudget price
Holds 3-inch tablets with an adjustable vent. Keep it away from skimmers, ladders and vinyl it can rest against.
See options on Amazon (opens in a new tab) - FAS-DPD drop test kit (chlorine, pH, TA, CH, CYA)Mid-range price
A drop-count kit reads free chlorine to 0.5 ppm (or 0.2 ppm), plus pH, alkalinity, calcium and stabilizer. Every dose on this site starts from a test, so this is the one thing worth buying first.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many chlorine tablets per week for a 10,000 gallon pool?
About 2–4 of the 3 inch (8 oz) tablets, depending on how much chlorine the pool uses: 2.6 a week at 2 ppm a day. See how many chlorine tablets for a 10,000 gallon pool.
How many chlorine tablets are in a 25 lb bucket?
About 50 if they are 8 oz tablets — one retailer lists about 100 tablets per 50 lb. Divide the bucket weight by the tablet weight printed on the label.
Do chlorine tablets raise stabilizer?
Yes. Trichlor adds about 0.6 ppm of cyanuric acid for every 1 ppm of chlorine. At 2 ppm a day that is about 8.5 ppm of CYA a week, which only leaves with water.
Can I put chlorine tablets in the skimmer?
It is not recommended. The dissolving tablet sends very acidic, chlorine-rich water straight through the pump, filter and any heater, which can corrode them. Use a floater or a feeder installed after the heater.
Why is my pool green even with tablets in the floater?
Usually because CYA has built up and the free chlorine is too low for that CYA level. Test both; if CYA is high, shock at the right level and consider partly draining. See how much liquid chlorine to SLAM a pool.
Related guides
Sources
- US EPA label 36284-5 — 3 in trichlor tablet (7 oz) (opens in a new tab) — 90% available chlorine; one tablet gives 4.7 ppm in 10,000 gallons; 1 tablet per 8,000 gallons every 7–14 days to maintain.
- ICC Building Safety Journal (PHTA Recreational Water Quality Committee) — Trichlor: the dependable pool performer (opens in a new tab) — Trichlor is 90% available chlorine and adds 0.6 ppm cyanuric acid for each ppm of chlorine.
- Leslie’s — In The Swim 3 inch chlorine tablets (50 lb) (opens in a new tab) — 99% trichlor, 90% available chlorine, about 100 tablets per 50 lb; gives both “one tablet per 10,000 gallons” and “one 3 inch tablet for every 5,000 gallons” as weekly rates.
- CDC — Model Aquatic Health Code, 5th edition (2024), code (opens in a new tab) — Free chlorine minimum 1.0 ppm (2.0 with CYA, 3.0 in spas); pH 7.0–7.8; CYA at or below 90 ppm; CYA:FC above 45:1 is an imminent hazard; TA 60–180 ppm; turnover tables.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- Trouble Free Pool (hobbyist forum wiki) — CYA/chlorine relationship (opens in a new tab) — A widely used hobbyist convention, not an official standard: minimum FC 7.5% of CYA, SLAM (shock) level 40% of CYA, salt-water pools 5%.
- CDC — Pool chemical safety: storage poster (opens in a new tab) — Separate acid and chlorine; don’t mix different types of chlorine; keep chemicals cool, dry and in original containers.