Swimming Pool Chemicals – What you need to know

If you are planning to have an indoor or outdoor pool installed, you will have to get to know the chemicals that are used to keep them clean. In this article we’ve laid out descriptions of the main chemicals involved and how they are used.


The most common of swimming pool chemicals, chlorine is used to ensure the water is germ-free and safe to swim in. It kills bacteria, viruses and the build-up of human sweat, as well as reducing the growth of algae. Chlorine is dispensed into the pool through a chlorinator and is available in stick, tablet, pellet and granule form.

Chlorine is available in two types: stabilised chlorine and unstabilised chlorine. Stabilised chlorine is used in outdoor pools and contains cyanuric acid. This acts as a stabiliser and stops the chlorine from being broken down by sunlight. Unstabilised chlorine does not contain cyanuric acid and is usually used in indoor pools.

If there is too much chlorine in the water then it can turn the water cloudy. In this case, when the water is checked, the free chlorine count will be found to be low and the chlorine has turned into chloramine (combined chlorine). If this has happened, the pool will need to be shocked by putting in double or three times the normal amount of chlorine.


Bromine is used as an alternative to chlorine in both indoor and outdoor pools, as well as spas and hot tubs. The reason for this is due to its broader pH range (which is a benefit in hard water areas) and less odour. Bromine is available in tablet form.


Algaecide is used to prevent the build-up of algae in a swimming pool. This is used as a prevention, not a cure as only shocking a pool will remove algae. It is recommended that at the beginning of every season you should add algaecide to the swimming pool water. Algaecide is available in tablet form.


Flocculants are used to help fix filtration problems. If small particles are escaping the filter, then adding flocculant to the water will help remove them. It works by clumping the fine particles together therefore making the new large particles easier to be picked up by the filter.

Water Balance Chemicals

These are a set of chemicals that can be used to control the levels of alkalinity, pH and calcium. They will help you achieve a water balance that is neither algae forming or corrosive. You can currently buy calcium and alkalinity builders, as well as pH increasers and reducers. These chemicals should be used carefully and in conjunction with proper water quality monitoring.


If you have accidentally put too much chlorine into your pool, you’ll need a dechlorinator. It is designed to safely remove chlorine from the pool.

Water Line Cleaner

Removes the build-up of scum from the waterline of the pool. The cleaner is non-acidic to avoid upsetting the chemical balance of the water in the pool.