Start with 2 tablets per week. Each 8-oz 3-inch trichlor tablet treats approximately 10,000 gallons. A 15,000-gallon pool sits between 1 and 2 tablets. Start at 2, test free chlorine twice per week, and adjust. Target: 1.0-4.0 ppm free chlorine at all times.
The “how many tablets” question does not have a single fixed answer because tablet consumption varies with temperature, sunlight, bather load, and CYA level. What matters is maintaining 1.0-4.0 ppm free chlorine per PHTA guidelines — the tablet count is just the lever you adjust to get there. Start with the calculated dose and test your way to the right number for your specific pool and conditions.
The Starting Calculation
3-Inch Tablet Dose for a 15,000-Gallon Pool
Standard rule: 1 tablet per 10,000 gallons
Your pool: 15,000 gallons
Calculation: 15,000 / 10,000 = 1.5 tablets
Since you cannot use half a tablet in a floater:
Start with 2 tablets (slightly more than the base rate)
Each 3-inch tablet weighs 8 oz (0.5 lb)
2 tablets = 1 lb of trichlor per week
1 lb trichlor adds ~6-7 ppm CYA per 10,000 gallons
For 15,000 gallons: 1 lb adds ~4-4.5 ppm CYA per week
✓ KEY FACT: These are starting points. Actual consumption depends on your pool’s specific conditions. Test free chlorine twice per week and adjust tablet count or floater opening to maintain 1.0-4.0 ppm free chlorine per PHTA guidelines.
Dose by Pool Volume: Reference Table
| Pool Volume | Base Tablet Count | Starting Point | Adjust If… |
| 5,000 gallons | 0.5 tablets | 1 tablet (use 1-inch tabs for better control) | FC stays above 3 ppm: reduce. FC drops below 1 ppm: increase. |
| 10,000 gallons | 1 tablet | 1 tablet per week (standard dose) | Same adjustment rule applies. |
| 12,000 gallons | 1.2 tablets | 1-2 tablets, start at 1, retest in 3 days | Same adjustment rule applies. |
| 15,000 gallons | 1.5 tablets | 2 tablets per week | Same adjustment rule applies. |
| 18,000 gallons | 1.8 tablets | 2 tablets per week | Same adjustment rule applies. |
| 20,000 gallons | 2.0 tablets | 2 tablets per week | Same adjustment rule applies. |
| 25,000 gallons | 2.5 tablets | 3 tablets per week | Same adjustment rule applies. |
| 30,000 gallons | 3.0 tablets | 3 tablets per week | Same adjustment rule applies. |
What Changes the Number of Tablets You Need
Temperature and sunlight
In hot, sunny weather above 85 degrees F, chlorine degradation accelerates. UV light destroys free chlorine faster, and warm water increases biological activity. During peak summer, you may need to increase to 3 tablets for a 15,000-gallon pool or open the floater valve wider. In spring and fall below 70 degrees F, 1 tablet may be sufficient.
CYA level
CYA protects chlorine from UV degradation — the higher the CYA (up to the 30-50 ppm target), the slower your tablets are consumed by sunlight. A pool with CYA at 40 ppm in direct sun will consume tablets slower than the same pool with CYA at 10 ppm. However, above 80 ppm CYA, chlorine effectiveness drops substantially even though FC readings look normal. Test CYA monthly and keep it in the 30-50 ppm range.
Bather load
Swimmers introduce ammonia, oils, and organic matter that consume free chlorine to form chloramines. A pool used by 2-3 people twice a week has very different chlorine demand than a pool used by 8-10 people daily. Heavy bather use weeks may require an extra tablet or additional liquid chlorine to maintain FC above 1.0 ppm.
Pool cover
A solar cover or safety cover dramatically reduces chlorine consumption. UV cannot reach the water surface, and evaporation — which carries some chlorine off — is reduced. Covered pools often need 30-50% fewer tablets than uncovered pools of the same size. If you switch to using a cover consistently, reduce tablet count and retest to avoid FC rising above 4.0 ppm.
How Many Tablets Per Season for a 15,000-Gallon Pool?
Full Season Tablet Estimate (20-Week Swim Season)
Starting point: 2 tablets per week
Season length: 20 weeks (typical US residential)
Base total: 2 x 20 = 40 tablets
Weight per tab: 8 oz = 0.5 lb
Total weight: 40 x 0.5 = 20 lbs
Seasonal CYA addition from those tablets:
~4-4.5 ppm CYA per week x 20 weeks = 80-90 ppm accumulated
This means by the end of a 20-week season using 2 tablets/week,
a 15,000-gallon pool starting with 0 CYA will approach 80-90 ppm —
near the upper limit. Test CYA at mid-season (week 10) and
plan a partial drain if CYA is approaching 70-80 ppm.
⚠ WARNING: The CYA accumulation math above is critical. A pool owner adding 2 tablets per week to a 15,000-gallon pool for 20 weeks without testing CYA will likely end the season with CYA near 80-90 ppm — at the edge of the range where chlorine effectiveness begins dropping significantly. Test CYA at opening, mid-season, and closing. Plan a partial drain if CYA exceeds 70 ppm.
A 25-lb Bucket vs. a 50-lb Bucket: How Long They Last
| Bucket Size | Number of 8-oz Tablets | Weeks at 2 tablets/week | Approx. Cost (Direct Supply 2026) |
| 10 lb | 20 tablets | 10 weeks | $40-55 |
| 25 lb | 50 tablets | 25 weeks (full season) | $55-75 |
| 50 lb | 100 tablets | 50 weeks (2 full seasons) | $100-130 |
Bottom Line: For a 15,000-gallon pool using 2 tablets per week over a 20-week season: a 25-lb bucket is exactly one season. A 50-lb bucket covers two full seasons and is the better value at $2.00-2.60 per pound versus $2.20-3.00 per pound for the 25-lb size.
If X Happens, Do Y
Free chlorine is consistently above 4 ppm even with only 1-2 tablets
Reduce tablet count or close the floater valve to reduce dissolution rate. Check whether the pool is covered — covers retain chlorine and cause FC to build up. Also verify the test kit is accurate — old or moisture-exposed test strips give false high readings. If FC genuinely is above 4 ppm consistently, the pool is being over-chlorinated and swimmers should not enter until FC drops.
Free chlorine drops to zero between tablet additions
The pool has high chlorine demand. In order of likelihood: CYA is too high (above 80 ppm) making chlorine less effective, active algae is consuming FC, heavy organic load from bather use or debris, or hot weather is accelerating both UV degradation and biological demand. Test CYA first. If CYA is in range, increase to 3 tablets and add supplemental liquid chlorine during peak use periods.
How do I know if I need 1-inch tablets or 3-inch tablets?
3-inch tablets (8 oz each) are designed for pools of 5,000 gallons or larger. They dissolve slowly over 5-7 days in a standard floater. 1-inch tablets dissolve much faster and are better suited for small above-ground pools under 5,000 gallons, spas, and situations where you need quick chlorine adjustment. For a 15,000-gallon pool, 3-inch tablets in a standard floater or inline feeder are the correct choice.
Related Guides
→ Pool Chlorine Tablet Buying Guide: What You’re Actually Paying For
→ The Pool Chemical Buying Guide: Everything You Need, Nothing You Don’t