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Swimming Pool & Spa Water Chemistry

Total Alkalinity

Total Alkalinity is the amount of alkaline substances in the water, the alkalinity level should be between 80-120ppm. If the total alkalinity level is out then it will have a bearing on the PH level and a true PH reading won't be possible. It is also known as TA.


The PH scale is the acid and alkaline scale, reading from 0 to 14, the neutral PH level is 7. In the swimming pool and spa industry  the PH level of the water should be 7.2. If the PH reading is lower than 7.2 then Sodium carbonate (PH increaser) should be added. If the PH reading is higher than 7.2 then dry acid (PH reducer) should be added. Phenol Red test tablets are used in PH testing.


In the swimming pool spa industry chlorine is categorised into three parts. Total Chlorine: the total amount of chlorine in the water,  Free Chlorine: The amount of chlorine still available to be used, Combined Chlorine: these are formed when free chlorine reacts with ammonia like compounds called amines. Most simple test kits read free chlorine, the level of free chlorine in the water should be between 2-3ppm in swimming pools and 4-5ppm in spas/hot tubs.If the free chlorine level is taken away from the total chlorine level then you will get the combined chlorine level in the water. DPD1 test tablets are used for free chlorine and DPD3 test tablets are used for total chlorine.


Bromine is an alternative to chlorine, it is a sanitiser that is more widely used in spas and hottubs than chlorine due to it being more stable in hotter water temperatures.Bromine is often used when sensitive skin is an issue. The bromine level of a swimming pool should be 2-4ppm and in a spa/hot tub it should be 3-5ppm.

Chlorine Shock

When using chlorine as a sanitiser it is important to use a chlorine shock treatment. This product is either sodium hypochlorite or calcium hypochlorite, we use this for two reasons firstly; a stabilised chlorine substance (tablets or granular)is use on a regular basis to keep the chlorine at the recommended level, but after a while the bacteria will get used to this so, we use the shock treatment to bring the chlorine level up to kill the bacteria. The shock treatment is also used to kill the chloromines in the water,. Chloromines are poor disinfectants and reduce the power of free chlorine and cause red eyes and bad odours.


Algaecides work alongside sanitisers to prevent the growth of algae. There are two types of algaecide, one is copper-free, this is used to prevent the algae growth and the other is copper based which, not only prevents algae it can a kill it as well. But copper based products are harmful to swimming pool and spa/hot tub equipment like heat exchangers.

Water Clarifiers and Flocculants

Water clarifiers and flocculants work in much the same way, they clump together small particles of dirt together which are then trapped in the filter (or will drop to the floor to be vacuumed up, depending on the product)in turn this will then make the swimming pool or spa water much clearer, giving that crystal clear water effect.


Phosphates are chemical compounds that contain phosphous, oxygen and sometimes hydrogen, this is essentially a nutrient source for algae, the get into to the pool via many different ways; leaves, bugs, dirt, swimmers and topping up the water level are just some of the ways. To get rid of phosphates a phosphate remover is needed.

The above is only the basic chemicals needed to maintain the water in your swimming pool or spa/hot tub. If you need more advise please dont hesitate to contact us on 01684 292211 or click here to message us

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