Pool Chlorine Types: Granular, Tablets, Liquid or Salt?

Every type of pool chlorine does the same basic job: it puts free chlorine into the water to kill algae and bacteria. Where they differ is in everything else they bring with them. Some raise pH, some lower it, some add calcium, and some add stabiliser that builds up season after season. On the Highveld, where municipal water is already hard and summer sun burns chlorine off quickly, choosing the right type for the job makes the rest of pool care much easier.

Calcium hypochlorite granules

Calcium hypochlorite is the familiar granular chlorine sold in tubs and buckets. It is strong, fast-acting and widely used both for daily dosing and for shocking.

  • Unstabilised. It contains no cyanuric acid, so on its own it is burnt off by strong sun fairly quickly. That makes it a good choice for shocking, and it does not add to stabiliser build-up.
  • Adds calcium. Every dose raises calcium hardness a little. Municipal water in Centurion and Pretoria is already hard, so over a season this can push calcium above the 200–400 ppm range and contribute to scale on the tile line, in the filter and on chlorinator cells.
  • Raises pH slightly. Expect to add a little acid now and then to keep pH at 7.2–7.6.
  • Dissolve it first. Granules thrown straight onto a plaster or marbelite floor can bleach or mark the surface. Dissolve the dose in a bucket of pool water, adding the chlorine to the water and not the other way round, and pour it around the pool with the pump running.

Add it in the evening, so it has the night to work before the sun gets to it.

Stabilised granules (dichlor)

Stabilised granular chlorine, usually sodium dichloroisocyanurate or dichlor, contains cyanuric acid built in. It dissolves quickly and has a roughly neutral effect on pH, which makes it easy to use.

The trade-off is stabiliser. Each dose adds cyanuric acid to the water, and unlike chlorine, it does not get used up. Used every day through summer, dichlor can push stabiliser well above the recommended range. It is handy for topping up and for pools that need a quick, gentle dose, but it works best alongside an unstabilised product rather than as the only chlorine you use.

Slow-release tablets (trichlor)

Chlorine tablets, usually trichloroisocyanuric acid or trichlor, dissolve slowly and release chlorine steadily over days. They are convenient for keeping a baseline level between checks.

  • Acidic. Trichlor has a very low pH, so it pulls pool pH and total alkalinity down over time. Keep an eye on both.
  • Adds stabiliser. Like dichlor, trichlor carries cyanuric acid into the water with every tablet, so stabiliser climbs steadily in a pool dosed only with tablets.
  • Use a floater or dispenser. Put tablets in a floating dispenser or an in-line feeder designed for them. Do not put them in the weir or pump basket unless your equipment manual says that is allowed. Concentrated, acidic water passing through the pump, the filter and any heat pump can corrode metal parts and damage seals.
  • Never let a tablet sit on the pool floor. It bleaches and damages plaster and marbelite, and marks fibreglass and vinyl.

Liquid chlorine (sodium hypochlorite)

Liquid chlorine is sodium hypochlorite, the same active ingredient as household bleach but stronger. It is easy to pour, dissolves instantly and leaves no residue, which makes it popular for larger pools and for shocking.

  • Raises pH. Liquid chlorine is strongly alkaline, so pH creeps up with regular use. Plan to add acid to keep it at 7.2–7.6.
  • Adds a little salt. Over time it slowly raises the salt content of the water. This is not usually a problem.
  • Short shelf life. Liquid chlorine loses strength quickly, especially in heat and sunlight. A drum left in a hot garage over summer can be much weaker than the label suggests. Buy what you will use soon and store it somewhere cool and shaded.
  • Unstabilised. Like calcium hypochlorite, it burns off in the sun and does not add to stabiliser.

Salt chlorination

A salt chlorinator makes chlorine from salt dissolved in the pool water, using an electrolytic cell. You add salt occasionally, and the chlorinator produces chlorine continuously while the pump runs. It removes most of the daily handling of chlorine, though pH tends to rise and the cell needs cleaning, especially with hard water.

We have compared the two approaches in detail in our post on salt chlorinators versus traditional chlorine, so we will not repeat it here. For salt levels and stabiliser in a salt pool, follow your chlorinator's manual.

Stabiliser build-up and why it matters

Stabiliser, or cyanuric acid, protects chlorine from being broken down by sunlight. In a sunny climate like ours, some stabiliser is useful: 30–50 ppm is the usual range for a chlorine pool. Without it, unstabilised chlorine can disappear in an afternoon.

The problem is that stabiliser does not evaporate or get used up. Every dose of dichlor or trichlor adds more. Above the recommended range, stabiliser starts to hold on to chlorine so tightly that the chlorine becomes sluggish. Your test kit may show a normal free chlorine reading while the pool still grows algae. The pool seems to need more and more chlorine to stay clear, and shocking works less well.

There is no chemical that removes stabiliser. The only practical way to bring it down is to partially drain the pool and refill with fresh water, which Highveld rain does a little of in summer. So:

  • Test stabiliser a few times a season, not just chlorine and pH
  • If you use tablets for daily dosing, use an unstabilised product for shocking
  • If stabiliser is already high, switch to unstabilised chlorine until it comes down

Our guide to pool water balance on the Highveld explains how stabiliser, pH, alkalinity and calcium fit together.

Which one should you use?

There is no single right answer. A practical combination for many home pools in Gauteng is slow-release tablets in a floater for the baseline, with calcium hypochlorite or liquid chlorine for shocking, and regular testing of pH, alkalinity and stabiliser. If calcium hardness is already high, liquid chlorine is kinder to it than calcium hypochlorite. If you have a salt chlorinator, you will mainly need an unstabilised product for the occasional shock after storms or heavy use.

Safe storage and handling

Pool chlorine is a strong oxidiser, and handling it carelessly causes fires, burns and toxic gas.

  • Never mix chemicals. Do not mix different types of chlorine with each other, for example calcium hypochlorite with trichlor tablets. The reaction can be violent and can cause fire.
  • Never let chlorine and acid come into contact. Mixing them releases chlorine gas.
  • Add chemical to water, never water to chemical. Always pour the product into a bucket of water, not water onto a heap of granules.
  • Use a clean, dry scoop for each product, and never use the same bucket for acid and chlorine.
  • Store cool, dry and shaded, in the original, clearly labelled container with the lid closed. Heat and moisture make chlorine unstable.
  • Store acid and chlorine apart, ideally on different sides of the storeroom, so a leak or spill from one cannot reach the other.
  • Keep them locked away from children and pets, off the floor and out of reach.
  • Wear gloves and eye protection, and wash your hands afterwards. Follow the label for first aid and disposal.

Where to get chlorine and help

At the moment, pool chemicals are ordered from us on WhatsApp rather than through the online checkout. Our pool shop in Centurion page explains what can be bought online and what is ordered on WhatsApp. Send your pool size and what you are using at the moment to 081 577 5051, and we can suggest the right products and quantities.

If you would rather not handle chemicals at all, a weekly pool maintenance plan puts testing and dosing in our hands; what is included is set out in your written quote.

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