The short answer: tablets are a convenience you pay for in stabilizer, and liquid chlorine is an errand you run to avoid that bill. Which trade is right depends on how often you're at the pool and how long your water stays in it — not on which product the person advising you happens to stock.
Almost every comparison you'll find online is published by a company selling chlorine. The retailers who sell both conclude you should use both. The liquid manufacturers conclude you should use liquid. What none of them do is the arithmetic, so let's start there.
What they actually are
| Liquid chlorine | Tablets (trichlor) | |
|---|---|---|
| Chemical | Sodium hypochlorite, 10–12.5% | Trichloroisocyanuric acid, ~90% available chlorine |
| Speed | Dissolved in seconds | Days, by design |
| Leaves behind | A trace of salt | Cyanuric acid, permanently |
| Effect on pH | Net neutral over the full cycle | Acidic — lowers pH and alkalinity continuously |
| Shelf life | Weeks to months; degrades in heat | Years, sealed and dry |
| Effort | Pour every few days | Refill a floater every week or two |
The arithmetic nobody shows you
Every 10 ppm of chlorine from trichlor also adds about 6.1 ppm of CYA. That sounds small. Run it forward for a pool consuming a typical 2 ppm of chlorine a day, starting the season at a healthy CYA of 40:
| After | CYA | Your FC target becomes | Situation |
|---|---|---|---|
| 1 month on tablets | 77 ppm | 9 ppm | Getting expensive |
| 2 months on tablets | 113 ppm | 13 ppm | Hard to hold; shock is impractical |
| 3 months on tablets | 150 ppm | 17 ppm | Drain required |
| 4 months on tablets | 186 ppm | 21.5 ppm | Drain required |
That's the entire story of the pool that opened in May looking perfect and went green in August while its owner did nothing differently. Nothing broke. The floater did exactly what the bucket promised, and each month it quietly raised the amount of chlorine that pool needed — until the level they'd always held was no longer enough. Dichlor is worse still, at about 55 ppm of CYA a month at the same demand.
CYA doesn't evaporate, doesn't break down in season, and isn't consumed. The only way out is replacing water. So the true cost of a season on tablets isn't the bucket — it's the bucket plus a partial drain, plus the water bill, plus rebalancing everything afterwards. That's the comparison the packaging never invites you to make.
What about cost?
Per unit of chlorine delivered, tablets and liquid land closer together than people expect, and local prices swing it either way. Tablets are more concentrated — you're not paying to ship water — but they're also a processed product with a premium attached. Liquid is cheap per gallon and expensive per mile if you're driving to fetch it.
The honest way to settle it is to compare cost per ppm of chlorine delivered into your pool, which is what the strength converter does with your local prices. Just remember to add the drain to the tablet column when the season ends — that's the line item that decides it, and it never appears on a shelf tag.
When tablets genuinely win
This is where most anti-tablet writing gets dishonest, so plainly: there are situations where tablets are simply the right answer.
- You travel, or the pool is at a second home. Chlorine that feeds itself for a fortnight beats perfect chemistry you aren't there to maintain. An unattended pool with tablets beats an unattended pool with nothing, every time.
- Your fill water is very alkaline. Trichlor is acidic, so it pushes back against a pH that climbs constantly — doing a job you'd otherwise pay for in muriatic acid.
- You drain and refill annually anyway. If the water is replaced each season — common in parts of the Southwest — the CYA accumulation resets before it becomes a problem, and the trade is genuinely fine.
- Your CYA is genuinely low and needs to come up. Then the stabilizer is a feature, and pucks do two jobs at once.
When liquid wins
- You're at the pool anyway. If you're testing a couple of times a week regardless, pouring a jug adds a minute and costs you nothing in stabilizer.
- Your CYA is already at or above target. At that point every puck makes your pool harder to manage, permanently.
- You're fighting algae. A SLAM means repeated dosing to a high level. Doing that on trichlor raises the shock level you're chasing — you'd be moving the finish line with every scoop.
- You have a salt system. The cell already makes chlorine; pucks add CYA the cell never needed and push you out of the SWG range.
This one is repeated everywhere and it's misleading. Sodium hypochlorite is strongly alkaline in the jug, so pH ticks up when you pour it — but as that chlorine is used up, the reaction reverses most of the rise. Over the full cycle it's close to pH-neutral. What genuinely moves your pH long term is trichlor, in the other direction: it's acidic, and a season of pucks steadily drags pH and alkalinity down. If you're topping up alkalinity all summer, your chlorine source may be why.
What about cal-hypo and granular chlorine?
Framing this as a two-way choice leaves out the third shelf. Calcium hypochlorite — cal-hypo, sold as granular shock at 65–73% — is the other common option, and it sits in an interesting middle: like liquid, it adds no stabilizer; unlike liquid, it stores for years and ships without the water.
Its passenger is calcium. Every 10 ppm of chlorine from cal-hypo adds roughly 7 ppm of calcium hardness, which accumulates exactly the way CYA does and leaves the same way — with the water. Whether that matters depends entirely on where you live. On soft fill water with a vinyl liner it's close to free. In hard-water regions where fill water already arrives at 300 ppm, it's the same trap as trichlor wearing different clothes.
| Source | Adds | Best when |
|---|---|---|
| Liquid chlorine | Trace salt only | You're there regularly — the default for most pools |
| Trichlor tablets | CYA, permanently | You're away, or CYA genuinely needs raising |
| Cal-hypo granular | Calcium hardness | Soft fill water, and you want shelf life without CYA |
| Dichlor granular | CYA, fastest of all | Rarely — spas, or a one-off dose |
One handling note specific to cal-hypo: it doesn't fully dissolve on contact, and undissolved granules sitting on a vinyl liner will bleach it. Pre-dissolve in a bucket of pool water — and never in the same bucket you've used for anything else.
Storage and shelf life
This is the quiet advantage tablets hold, and it's worth being straight about. Sealed, dry trichlor keeps for years with barely any loss. Liquid chlorine degrades from the day it's made — faster when it's hot, faster when it's strong, and faster in sunlight. A 12.5% jug that spent a summer month on a hot pallet can test weaker than fresh 10%.
Practically, that means buying liquid the way you'd buy milk: from a supplier with turnover, in quantities you'll use within a few weeks, stored somewhere cool and dark. If your only option is a jug of unknown age from a hot shelf, tablets or cal-hypo may genuinely deliver more chlorine per dollar than the label suggests. And it's a real argument for buying liquid locally and often rather than stockpiling it in the garage in April.
So which should you use?
| If this is you | Use |
|---|---|
| At the pool most days, CYA already 30+ | Liquid chlorine |
| Away for a week or more at a time | Tablets while away, liquid when home |
| Salt water pool | The cell, with liquid for shocking |
| CYA under 30 and needs raising | Tablets, until CYA reaches target — then switch |
| Fighting algae right now | Liquid chlorine, exclusively |
| CYA already above 80 | Liquid chlorine, and plan a partial drain |
Notice that most rows are a rule about your pool rather than a verdict on the products. That's the honest shape of this question: tablets aren't bad, they're a loan. Take one deliberately, for a reason, and repay it before it compounds — rather than letting a floater make the decision every day for five months.
The approach most experienced owners land on
Liquid as the daily driver, tablets kept on the shelf for vacations, and CYA tested monthly so the loan never quietly grows. When CYA drifts toward the top of its range, the pucks go away until a partial drain or winter rain brings it back down.
That's not a compromise for its own sake — it's using each product for the thing it's genuinely good at. Tablets are an excellent way to keep a pool alive while you're not there. They're a poor way to run a pool you're standing next to, and the stabilizer calculator will tell you exactly what it's cost you if you've been doing it a while.
Two safety notes that outrank all of this
Never mix them. Not in a bucket, not in a floater, not in the same scoop, and not in storage where a leak could bring them together. Trichlor and sodium hypochlorite react violently and can produce chlorine gas. Keep them apart and keep both away from acid.
Never put tablets in the skimmer. It's a common shortcut and it sends highly acidic, highly concentrated water straight through your pump and heater whenever the pump is off. Use a floater or an inline chlorinator designed for the job.