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Pool Chemistry 101-B: Know Your Chemicals

Updated: Jan 2, 2021

Whether you’ve just got your first swimming pool or hot tub or if you’ve had it a while, the chemicals that you need to add into your water can be confusing for many. There are lots of names and terms, dosage rates, and other information to get your head around. Eventually many people will get into a routine of adding certain things to have certain effects, but with little understanding of why.


Below, we have laid out the most common swimming pool and spa/hot tub chemicals, with their descriptions and uses, plus included their alternative names. If there is a chemical or product that isn’t included here in our list of common swimming pool and spa chemicals that you have a question about or think we should add then please let us know at enquiries@energiseleisure.co.uk.


In other posts in our Water Chemistry 101 series, we explore these chemicals in detail for those who would like to learn more, take a look at Balanced Water Basics, How Chlorine Works, Testing, Pool and Spa Terminology, and more.


N.B. When handling any chemicals, we recommend using relevant PPE to prevent injury or irritation – gloves are a minimum for all products, but consider the splash/spillage risk and consider eye and clothing protection, sometimes even respirators.

Let’s begin…

Sanitisers and Disinfectants

A swimming pool or hot tub sanitiser or disinfectant is a general term that applies to a range of chemicals added to your water to “clean” it of harmful bacteria and other pathogens.


(n.b. the pH and available content figures given are approximate, "typical" values which may vary between brands and dilution levels)



Sodium Hypochlorite/Liquid Chlorine/NaOCl/Bleach – a liquid product most used with automatic dosing systems, although some pool engineers will use it manually. We do not recommend manual use of Liquid Chlorine due to its high hazard level.

pH Level: 12-13 (will raise your water’s pH)

Available chlorine content: usually between 10-15%, but with minimal impurities




Calcium Hypochlorite/Shock/Rapid Shock – often granular, but available in tablet or small “briquette” form. Can be added manually and is used in feeder and automatic dosing systems. Not suitable for general dosing in hard water areas due to effect on calcium hardness and total alkalinity. Ideal for indoor pools (un-stabilised) and tiled pools in soft water areas where hardness and alkalinity management is difficult (predominantly commercial environments).

pH Level: variable-high (will raise your water’s pH)

Available chlorine content: usually around 70%



Stabilised Chlorine Tablets /Trichlor/Trichloroisocyanuric Acid – large or small tablets often placed into a table feeder or “floater” to maintain chlorine residual over long periods of time. Contains stabiliser (cyanuric acid) to protect chlorine from UV “burn off” in outdoor swimming pools and spas/hot tubs. We do not recommend using stabilised chlorine for indoor pools or to “shock” your water.

pH Level: 3 (will lower your water’s pH)

Available chlorine content: 87-90%



Stabilised Chlorine Granules/Dichlor – granular chlorine that resembles small balls (and is easily spilled). Usually added manually to the water to “top up” chlorine levels when they fall low. Contains stabiliser (cyanuric acid) to protect chlorine from UV “burn off” in outdoor swimming pools and spas/hot tubs. We do not recommend using stabilised chlorine for indoor pools or to “shock” your water.

pH Level: 7/Neutral (little to no effect on pH)

Available chlorine content: 55%



Multifunctional Chlorine (Tablets or Granules) – Same as stabilised chlorine tablets and granules, with additional algicide and clarifier. Great for overall management and water health for outdoor swimming pools. Check your brand to find out the exact contents.

pH Level (Tablets): slightly higher than normal Trichlor (lowers pH to lesser degree)

pH Level (Granules): 7/Neutral (little to no effect on pH

Available chlorine content: variable, slightly less than normal stabilised versions.


Bromine Tablets – chlorine alternative. Effectiveness is less affected by the water’s pH and temperature than chlorine and byproducts are less harmful/irritating. Unlike chlorine, byproducts aid disinfection and can be “reactivated” when water is shocked. Not usually referred to by an alternative name and works the same way as chlorine tablets. Recommended for spas and those with sensitive skin.

pH Level: 4 (will lower pH)

Available Bromine content: approx. 60%


Bromine Granules - chlorine alternative, but still contains dichlor (full name is bromochlorodimethylhydantoin or BCDMH). Effectiveness is less affected by the water’s pH and temperature than chlorine and byproducts are less harmful/irritating. Unlike chlorine, byproducts aid disinfection and can be “reactivated” when water is shocked. Not usually referred to by an alternative name and works the same way as chlorine granules. Recommended for spas and those with sensitive skin. Bromine should not be added to a pool containing a readable chlorine level.

pH Level: 7/Neutral (little to no effect on pH)

Available Bromine content: 10% + 90% dichlor



Honourable Mention – correctly specified secondary disinfection systems such as UV and Ozone generators can minimise sanitiser usage and are effective against the most common chlorine-resistant pathogens found in swimming pool and spa water. Commercial UV systems and ozone oxidise harmful byproducts and ozone has a flocculant effect which boosts filtration and water clarity.

Oxidisers and Shock Products

Oxidisers are chemicals that remove harmful disinfection byproducts and other organic materials by breaking them down. They should be used before first use, after especially heavy use (think pool party or all-day family session), if your water becomes cloudy, green or otherwise problematic, or if your sanitiser residual reaches zero.

Chlorine Shock – see Calcium Hypochlorite Granules.

Rapid Shock – see Calcium Hypochlorite Granules.

Non-Chlorine Shock – a chlorine-free alternative commonly used in spas/hot tubs and bromine swimming pools. Available in single-use sachets as opposed to bulk containers.

Hydrogen Peroxide/H2O2/Liquid Oxygen/Active Oxygen – a hazardous liquid oxidiser most used for commercial pools to manage disinfection byproducts. Requires an automated dosing system as it should not be dosed manually and is more heavily regulated than most other swimming pool chemicals.

pH Regulation

pH is a logarithmic scale which measures the “potential” or “power of” hydrogen level of the water – greater availability of hydrogen ions the more acidic something is – and the lower the pH value. pH 7 is neutral and above 7 is “basic” or “alkali”. The scale works by displaying availability of H+ ions compared to pure water – so pH7 has the same amount as pure water, acids have more H+, and alkaline solutions have less H+ than pure water.


pH Increaser/pH+/Soda Ash/Sodium Carbonate/Na2CO3 – a solid, granular alkali which dissolves in water and raises pH. Commonly manually dosed in domestic swimming pools, spas, and hot tubs, or can be pre-dissolved for use in commercial automatic chemical dosing systems, although this often isn’t necessary due to the pH of sanitisers.






Sodium Hydroxide/Liquid pH+/Caustic Soda Liquid/NaOH - a hazardous liquid used mainly in commercial applications for pH adjustment and other areas.


pH Decreaser/pH Reducer/pH-/Dry Acid/Sodium Bisulphate/Sodium Hydrogen Sulphate - a solid, granular acidic compound which dissolves in water and lowers pH. Commonly manually dosed in domestic swimming pools, spas, and hot tubs, or can be pre-dissolved for use in commercial automatic chemical dosing systems.


Hydrochloric Acid/Liquid pH-/HCl – liquid pH adjustment used in automatic chemical dosing systems. Readily available at lower concentrations and considered safer than Sulphiric Acid. Also used for scale removal and as a cover, tile, and floor cleaning product at low concentrations.


Sulphuric Acid/Liquid pH-/H2SO4 – liquid pH adjustment, highly hazardous and more regulated than HCl.



(Total) Alkalinity Increaser/Sodium Bicarbonate/Baking Soda/Bicarbonate of Soda – not strictly a pH regulation chemical, but the total alkalinity (TA) of water is said to act as a “buffer” for pH. At the simplest level, the higher your alkalinity levels are the more difficult it is to affect your pH with the two previous chemical types. Low alkalinity leaves you vulnerable to pH “swing” where it becomes difficult to adjust to the correct levels. Solid, powdered compound.


(Total) Alkalinity Decreaser – while there are products that do this, it is common practice to use pH- with a different dose rate and method to lower alkalinity due to effects on pH and to save on having yet another chemical in your cupboard to worry about.

Water Clarity

Clarifiers and Flocculants – these bind small particles together that allow them to be picked up by your filter of vacuumed off the filter. If your water looks slightly murky then this could be the option for you. Available as liquids, jellies, and tablets.




Algaecides/Algicides – a variety of different types of algaecide are available in long term and “killer” variants, with or with copper. As the name suggests, they are designed to prevent or kill algae growth and don’t usually cause a pool or spa to be unusable after application. “Wintertime” algaecide is especially useful to and recommended for those who shut their swimming pool down over the winter months.


No Foam/Foam Away/Foam Remover – usually reserved for use in spas and hot tubs, if you begin to have foam or bubbles forming on the surface of your water then you should reach for some of this. You should only need a small amount. Available as a liquid.

Miscellaneous

Chlorine Reducer – if you have elevated chlorine levels you can use this to bring it down, but most will simply leave their swimming pool or spa uncovered and/or wait a while before use and allow the chlorine to “burn off”. Usually only used before disposal – especially in areas where chlorinated water is not permitted to be drained away. This can also be used to lower bromine levels.


Stain and Scale Inhibitor/Remover – there are a variety of products available, including specialist products aimed specifically at water with high metal content. High pH, alkalinity, or Calcium Hardness each increase the chance of calcium scale/limescale forming and these products help prevent or remove scale with minimal or no effect on pH. Liners, some tiles, and grout are susceptible to staining so these products are useful in outdoor swimming pools where a lot of debris ingress is found or any pool with high metal content.


Hot Tub Flush/Biofilm Killer/Swirl Away/Pipe Cleaner – biofilm is resistant to chlorine and can be incredibly harmful to those who bathe in infected water. Depending on the type of product, you can use these to tackle biofilm, clean other dirt and debris from pipes, and descale.


Various other cleaning products such as tidemark cleaner, stain remover, tile and grout cleaner, filter cleaners, etc are available also in a variety of formats.


Hydrochloric Acid/Scale Remover/Cover Cleaner/HCl – liquid pH adjustment used in automatic chemical dosing systems. Readily available at lower concentrations and considered safer than Sulphiric Acid. Also used for scale removal and as a cover, tile, and floor cleaning product at low concentrations.

Chlorine Stabiliser/Cyanuric Acid/CYA – granules that are added to boost stabiliser levels in outdoor pools, usually only required when unstabilised sanitisers are being used such as sodium or calcium hypochlorite. Also a consideration for unstabilised indoor pools with UV systems.


For more chemical advice or to get a quote, call us on 0333 577 9692 or email enquiries@energiseleisure.co.uk. Please note that Energise Leisure Ltd is currently only able to offer chemicals in “box quantities” which vary depending on the product.

If there is a chemical or product that isn’t included here in our list of common swimming pool and spa chemicals that you have a question about or think we should add then please let us know!

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