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They're all "chlorine," so does it matter which you buy? It does. Each type has a different strength, pH, and whether it adds stabilizer or calcium — and that decides when you'd reach for it. Here's the plain-English breakdown.
Standing in the pool aisle staring at bags and buckets labeled trichlor, dichlor, and cal-hypo is genuinely confusing — they all sanitize, but they behave very differently once they hit the water. Pick the wrong one for the job and you can send your pH swinging, drive your stabilizer through the roof, or waste money on the weaker option. Here's exactly what separates them and when to use each.
Quick answer: the comparison at a glance
| Type | Available chlorine | Adds stabilizer (CYA)? | Effect on pH | Speed | Best use |
|---|---|---|---|---|---|
| Trichlor (tablets) | ~90% | Yes | Lowers (acidic) | Slow | Everyday sanitizing in a floater/feeder |
| Dichlor (granular) | ~55–62% | Yes | Near-neutral | Fast | Spot treatment & quick boosts |
| Cal-Hypo (granular) | ~65–73% | No | Raises | Fast | Shocking, esp. when CYA is high |
| Liquid (sodium hypochlorite) | ~10–12% | No | Raises | Instant | Shocking large volumes, no residue |
The key concept: stabilized vs. unstabilized
Master this one idea and the whole chart makes sense. Stabilizer (cyanuric acid, or CYA) is sunscreen for chlorine. Without it, UV rays destroy free chlorine within hours, so every outdoor pool needs some — around 30 to 50 ppm.
- Stabilized chlorine (trichlor & dichlor) already contains CYA. Great for everyday outdoor use — but every dose adds a little more stabilizer. Let it climb too high (much above 50 ppm) and chlorine gets "locked" and loses its punch, eventually forcing you to dilute with fresh water.
- Unstabilized chlorine (cal-hypo & liquid) contains no CYA. Perfect for shocking and for topping up chlorine when your stabilizer is already high — but on its own in the sun, it burns off fast.
The pro combo
Most well-run pools use both: a stabilized product (trichlor tablets) for daily sanitizing, plus an unstabilized product (cal-hypo or liquid) for weekly shocking. You get sun protection without letting stabilizer run away on you.
Trichlor: the everyday workhorse
At about 90% available chlorine, trichlor is the strongest common form and comes as hard, slow-dissolving tablets. That slow dissolve is exactly what you want for hands-off, week-long sanitizing in a floating dispenser or an automatic feeder. Two things to manage: it's acidic, so it gradually lowers pH (keep a pH increaser handy), and it slowly adds CYA. It's built for steady sanitizing, not for shocking — it dissolves far too slowly for that.
Trichlor done rightPoolTabit 3-inch trichlor tablets in 5, 10, 25 and 40 lb buckets — commercial strength, at a fair price per pound.
Shop Chlorine Tablets
New to tablets? Our guide on how to use 3-inch chlorine tablets covers dosing and placement in detail.
Dichlor: the fast, gentle granular
Dichlor is a stabilized granular chlorine at roughly 55 to 62% strength, with a near-neutral pH that won't swing your balance. Because it dissolves quickly, it shines for spot-treating a problem area or giving chlorine a fast boost without the pH drop that trichlor causes. The catch is the same as trichlor: it adds CYA with every use, so it's not the one to lean on if your stabilizer is already high. It also tends to cost more per pound of actual chlorine.
Cal-Hypo: the shock specialist
Calcium hypochlorite delivers a fast, powerful hit of chlorine at about 65 to 73% strength and adds no stabilizer — which makes it the go-to for shocking, especially when your CYA is already high and you can't afford to add more. Two things to watch: it raises pH (you may need a pH decreaser afterward), and it adds calcium hardness, so go easy in hard-water areas. Pre-dissolve it in a bucket of water before adding, per the label, so it doesn't settle and bleach your surface.
Never mix chlorine types
Do not combine trichlor and cal-hypo — or any two different chlorine products — in the same feeder, bucket, or scoop. The reaction can generate intense heat, fire, or toxic gas. Use one product per device, add each to the pool water separately, and store them well apart.
So which should you use?
Match the product to the situation:
- Everyday sanitizing, outdoor pool: trichlor tablets in a floater or feeder, plus a weekly cal-hypo or liquid shock. This is the standard, reliable combo.
- Your CYA is already high: switch shocking and top-ups to cal-hypo or liquid so you stop adding stabilizer.
- Small pool or spa, or you want no pH swing: dichlor for quick, near-neutral spot dosing.
- Hard water / high calcium: avoid cal-hypo for routine use; reach for liquid chlorine to shock instead.
- Indoor pool (little to no sun): you need far less stabilizer, so unstabilized options work well.
Wherever you land, fold your choice into a consistent routine — our weekly pool maintenance schedule shows how sanitizing and shocking fit together across the week. Browse shock and balancers on our pool chemicals page.
Frequently asked questions
What is the difference between trichlor and dichlor?
Both are stabilized chlorines that add cyanuric acid. Trichlor is ~90% chlorine, comes as slow-dissolving acidic tablets, and is ideal for everyday sanitizing in a floater or feeder. Dichlor is ~55–62% chlorine, comes as fast-dissolving near-neutral granules, and suits spot treatments and quick boosts.
Is cal-hypo or dichlor better for shocking?
It depends on your CYA. If stabilizer is already high, cal-hypo is better since it adds none (though it raises pH and adds calcium). If stabilizer is low and you want near-neutral pH, dichlor works — but every dose also raises CYA.
Can I use tablets and shock from different brands together?
Different products from different brands are fine, but never mix them in the same feeder, bucket, or scoop. Combining chlorine types — especially trichlor and cal-hypo — can react dangerously. Add each to the water separately and store them apart.
Which pool chlorine doesn't raise cyanuric acid?
Cal-hypo and liquid chlorine (sodium hypochlorite) are unstabilized, so they add no CYA. They're the right choice when your stabilizer is already high and you need chlorine without pushing it higher.
Why isn't my chlorine working even though the level looks high?
Usually very high cyanuric acid (which locks up chlorine) or high pH (which slows it down). Test both — if stabilizer is well above 50 ppm, dilute with fresh water, and bring pH back to 7.4–7.6.
This guide is general educational information. Chlorine choice and dosing vary by pool size, surface, and local water chemistry — always follow the directions on each product label and test your water before dosing.
