Liquid chlorine vs tablets vs cal-hypo
2026-09-04 · 8 min read
Every chlorine product delivers the same active ingredient and leaves something different behind. The choice is not really about chlorine — it is about which side effect you are prepared to manage.
Best overall
Liquid chlorine
Adds nothing but chlorine. The default for any pool already carrying stabiliser.
Best budget
Trichlor tablets
Cheapest per ppm and the least labour — until cyanuric acid hits the ceiling.
Best for large pools
Cal-hypo
Compact, storable, strong; watch calcium hardness in hard-water regions.
The four products, side by side
Our pick — liquid chlorine
| Product | Available Cl | 1 ppm / 10k gal | Adds | pH effect | Storage |
|---|---|---|---|---|---|
| Liquid chlorine 12.5% | 12.5% | 10.2 fl oz | Nothing | Slightly up, briefly | Weeks — it decays |
| Trichlor 90% | 90% | 1.5 oz | 0.6 ppm CYA per ppm | Strongly down | Years, sealed |
| Cal-hypo 73% | 73% | 1.8 oz | Calcium hardness | Up | Years, dry and cool |
| Dichlor 56% | 56% | 2.4 oz | 0.9 ppm CYA per ppm | Near neutral | Years, sealed |
Dose maths
Derived from trade strength, not a bucket label — the working is in the chlorine calculator.
The real cost
Not price per pound. It is what each product adds to the water over a season.
WHO ceiling
Free chlorine must not exceed 3 mg/L in public and semi-public pools.
Liquid chlorine
Sodium hypochlorite is chlorine and salt water. It adds no stabiliser, no calcium and no acid load, which makes it the only product you can use indefinitely without changing the water’s character. The costs are physical: it is heavy, it is bulky, and it loses strength on the shelf — a jug bought in June and used in August is not the jug the label describes.
For a route business this is usually the right default, because it keeps every other reading where you put it. Dose it at dusk with the chlorine calculator.
Trichlor tablets
Tablets are the easiest chlorination there is: load a feeder, walk away, come back in a week. They are also the reason most pools eventually need a partial drain. Every ppm of chlorine a trichlor tablet delivers leaves roughly 0.6 ppm of cyanuric acid behind, and the WHO guidance puts the ceiling at 100 mg/L. A pool run entirely on tablets crosses that in a season or two.
They are also strongly acidic, which pulls pH and alkalinity down steadily — the mirror image of a salt pool’s upward drift.
Cal-hypo
Calcium hypochlorite is strong, storable and the traditional choice for shocking. It adds calcium hardness, which is harmless in soft water and cumulative in hard water — the pool that clouds slightly after every shock is usually telling you it has had enough. Pre-dissolve it in a bucket rather than broadcasting it onto a vinyl floor.
Dichlor
Dichlor is stabilised, granular and near-neutral in pH, which makes it convenient for spot dosing and hot tubs. The stabiliser load is the highest of the four per ppm delivered, so it is a poor choice for routine use on an outdoor pool that already has CYA in it.
What most pools should actually do
Chlorinate routinely with liquid, keep cal-hypo for shocking a pool with room in its calcium hardness, and use tablets deliberately — for a fortnight of holiday cover, not as the standing method. Check stabiliser monthly and the decision makes itself.
Buying checklist
- Test cyanuric acid before choosing a product, not after.
- In hard water, count cal-hypo's calcium as a cost.
- Buy liquid chlorine in quantities you will use inside a month.
- Never store acid and any chlorine product in the same cabinet.
- If tablets are the plan, budget for a partial drain every second season.