Liquid chlorine vs tablets: pros and cons
Both get chlorine into your pool, but they're very different products with different side effects on your water chemistry. The choice between them matters more than most pool owners realize — especially when it comes to CYA buildup.
Quick comparison
| Liquid Chlorine (Bleach) | Trichlor Tablets | |
|---|---|---|
| Chemical name | Sodium hypochlorite | Trichloroisocyanuric acid |
| Available chlorine | 10–12.5% (pool-grade) | ~90% |
| Adds CYA? | No | Yes — about 6 ppm CYA per 10 ppm FC added |
| Effect on pH | Raises slightly | Lowers |
| Convenience | Must add daily or every other day | Set and forget for days |
| Storage | Heavy jugs, degrades over time, spills bleach clothes | Compact, long shelf life |
| Cost | Cheaper per season ($100–200) | More expensive ($200–400) |
| Best for | Pools where CYA is already at target | Starting the season when CYA is low |
The CYA problem with tablets
This is the single biggest reason experienced pool owners switch to liquid. Every trichlor tablet that dissolves in your pool adds cyanuric acid (CYA/stabilizer) along with the chlorine. You can't get one without the other.
Early in the season, this is actually helpful — CYA protects chlorine from UV sunlight, and you need some. But once CYA reaches your target (usually 30-50 ppm), every additional tablet pushes CYA higher with no way to bring it back down except draining water.
| Scenario | CYA Level | Chlorine Effectiveness | What To Do |
|---|---|---|---|
| Early season | 30–50 ppm | Optimal | Tablets are fine here |
| Mid season | 60–80 ppm | Reduced | Switch to liquid chlorine |
| Late season | 100+ ppm | Severely reduced | Partial drain needed to lower CYA |
The math on CYA buildup
A typical 15,000-gallon pool using trichlor tablets in a floater will see CYA rise by roughly 5-8 ppm per week during heavy summer use. Starting at CYA 30 in May, you could be at CYA 80+ by July. At that point, your chlorine is working at a fraction of its capacity even though the test reads "normal."
When to use tablets
Tablets aren't bad — they just have a specific window where they make sense:
- Opening the pool: CYA is usually low after winter. Tablets build it up while chlorinating
- CYA below 30 ppm: Your chlorine has no UV protection. Tablets solve both problems at once
- Vacation or travel: Drop tablets in a floater before you leave. They'll maintain chlorine for days without you
Once CYA hits 50 ppm, switch to liquid chlorine for the rest of the season.
When to use liquid chlorine
- CYA is at or above target: Liquid adds chlorine without adding any stabilizer
- Daily maintenance: Most cost-effective way to maintain FC day-to-day
- Shocking: Liquid chlorine is the cleanest way to shock — no CYA, no calcium, no residue
- Salt pools converting from tablets: If you switched to SWG but CYA is already high
Practical tips for liquid chlorine
- Buy pool-grade (10-12.5%). Regular household bleach (5-6%) works but you need twice as much
- Add it in the evening. Sunlight degrades chlorine immediately — adding at dusk gives it all night to work before UV hits
- Pour in front of a return jet for fast distribution, or pour along the edges of the deep end
- Use it within a month of purchase. Liquid chlorine degrades on the shelf — especially in heat. Fresh is always better
- It raises pH. Liquid chlorine has a pH of about 13. Plan to add a small amount of acid periodically to compensate
The bleach aisle shortcut
Regular unscented household bleach (sodium hypochlorite, no additives) is chemically identical to pool-grade liquid chlorine — just at a lower concentration (5-6% vs 10-12.5%). It works fine in a pinch, but pool-grade is more cost-effective because you use less. Never use bleach with fragrances, surfactants, or "splashless" formulas.
What about dichlor?
Dichlor (sodium dichloro-s-triazinetrione) is a granular chlorine that dissolves quickly. Like trichlor, it contains CYA — but it dissolves faster and is pH-neutral, making it popular for hot tubs and for initial pool startups.
The same CYA rule applies: use it when CYA is low, switch to liquid once you hit your target.
The best approach: use both
Most experienced pool owners don't pick one or the other — they use both strategically:
- Season start: Use trichlor tablets to build CYA from zero to 30-50 ppm
- Rest of season: Switch to liquid chlorine for daily maintenance
- Shocking: Always use liquid chlorine (no CYA, no calcium)
- Going on vacation: Tablets in a floater for hands-free chlorination
This gives you the convenience of tablets when you need it and the clean chemistry of liquid the rest of the time.
Track your CYA and chlorine together
PoolChem Tracker monitors your CYA level alongside FC, calculates dynamic chlorine targets based on your actual CYA, and warns you when it's time to switch from tablets to liquid — before CYA gets out of control.
Keep reading
- Pool Chlorine Levels Chart — what your FC, TC, and CC readings mean
- Saltwater vs Chlorine Pools — the full comparison of pool sanitizing systems
- Free Chlorine vs Total Chlorine — understand the three types of chlorine in your water
- Pool Chemistry for Beginners — the 5 numbers every pool owner should know