Maintaining Your Pool

How to maintain your home swimming pool

While nobody buys a pool to give themselves lots of extra work or revel in the complexities of pool chemistry, carrying out effective pool maintenance on a regular basis is a hugely important part of owning and operating a pool.

When it comes to the chemicals required to keep your pool healthy, there’s a long list of must-haves and optional extras that you need to know about. At, we offer an all-encompassing range of pool chemicals to see you through every season and every eventuality.

But where to start? What products do you need to maintain your pool? And how do you use them effectively? To help you wade through the myriad of dos and don’ts that pool maintenance brings with it, we’ve put together a comprehensive guide covering:

  • Swimming pool sanitisers
  • Shock Treatment
  • Water balancers
  • Algaecides
  • Flocculants
  • Swimming pool dechlorinators
  • Water Testing

Each topic will give you a complete breakdown of what the chemicals do and how to use them correctly, so you can get to grips with how to maintain your home swimming pool efficiently.

Swimming Pool Sanitisers

Swimming pool sanitisers are the most important group of chemicals for treating your pool. Their job is to quickly kill any bacteria or viruses that get into the water so that they cannot multiply and cause infections in swimmers. Consequently, they play a major role in maintaining pool water, keeping it clean and clear. There are two main sources of sanitisers - chlorine and bromine.


There are two types of chlorine available to use as sanitisers. These are stabilised and unstabilised chlorine.

Stabilised chlorine

Stabilised chlorine is predominantly used in outdoor pools. In order to stop chlorine being broken down by sunlight, it is combined with a stabiliser called cyanuric acid. Cyanuric acid can be added separately or, more commonly, it is supplied as stabilised chlorine granules or tablets.

What are stabilised chlorine granules?

Stabilised Chlorine Granules are a white granular solid that are added to the pool water via manually dosing your pool as and when needed. They have a close-to-neutral pH (7), so they will have little effect on the pH balance of the water. They are added to the pool water by dissolving the required amount in a bucket of warm water and distributing it around the pool.

User tip: to increase the free chlorine by 1ppm (parts per million), add 100 grams per 10,000 gallons.

What are stabilised chlorine tablets?

Stabilised Chlorine Tablets are provided in two tablet sizes: 20 grams and 200 grams. Twenty-gram tablets are designed for maintaining above-ground swimming pools (which are typically smaller) while 200-gram tablets are designed for larger in-ground pools with a larger volume of water. They are added to the water via a floating dispenser or the skimmer basket.

As chlorine tablets are slow-dissolving, they can be left in the pool, providing a constant chlorine dose at all times. This reduces the amount of work you have to do to maintain an adequate chlorine level. As chlorine tablets are slightly acidic, it’s important to keep an eye on your alkalinity and pH levels when using them.

User tip: for 20-gram tablets, fill up the floating dispenser and adjust the collar accordingly. The tablets will take 5-7 days to dissolve.

For 200-gram tablets, place one tablet per 11,000 gallons in the skimmer basket. It will take 3-5 days to dissolve. Alternatively, place one tablet per 7,000 gallons in the floating dispenser. It will take 10-14 days to dissolve.

What are multifunctional tablets?

Multifunctional Tablets are a type of stabilised chlorine tablet that work in exactly the same way as standard chlorine tablets. However, these tablets also have an algaecide and a flocculant built in - allowing you to reduce the chances of algae and cloudiness occurring while dosing your pool with chlorine. 

Unstabilised chlorine

Calcium hypochlorite, otherwise known as unstabilised chlorine, is chlorine that does not have cyanuric acid added to it. In the absence of cyanuric acid, unstabilised chlorine is more directly affected by the sun’s ultraviolet rays, meaning it dissipates more quickly, carries less sanitising power and needs to be added more often than stabilised chlorine to be effective.

Where unstabilised chlorine offers users an advantage is for use with indoor pools (where it is unaffected by direct sunlight), which can be negatively impacted by the high levels of cyanuric acid found in stabilised chlorine. Unstabilised chlorine can also be used as pool shock, or for quick chlorine dosing at times where your pool is in heavy use.

How to add calcium hypochlorite to a pool

Calcium hypochlorite is supplied in two forms: granules or tablets.

For those using calcium hypochlorite granules, the granules are dissolved in a bucket of warm water and poured into the skimmer basket of your pool. It’s important to pour the product into your skimmer basket rather than directly into your pool, as the granules will not completely dissolve in the bucket. Please make sure your skimmer is free from all other types of chlorine before pouring calcium hypochlorite granules into the skimmer.

For those using calcium hypochlorite tablets, the tablets are placed in the skimmer basket or floating dispenser.

User tip: 75 grams adds approximately 1ppm of free chlorine to 10,000 gallons of water.


Bromine – what is bromine in a pool?

Bromine is an alternative swimming pool sanitiser chemical to chlorine. Bromine offers a number of benefits for maintaining pool water, acting as a sanitiser, oxidiser and algaecide for your pool. While chlorine is the more common choice among pool owners, bromine is the chemical of preference for spa and hot-tub owners due to its superior effectiveness in warmer temperatures.

Using a brominator and BCDMH sanitiser (bromine tablets)

Some outdoor and indoor pools, as well as most spa pools, are fitted with circulation feeders called brominators. Brominators use a sanitiser called bromo-chloro-dimethyl hydantoin (BCDMH) to keep pool systems sanitised. BCDMH is supplied in the form of white tablets (bromine tablets) which are loaded into the brominator and then have the pool water pumped over them. BCDMH should not be added directly to your pool or through the skimmers.

You should monitor the level of active bromine in your pool with a bromine test kit and adjust your brominator to give a bromine level between 2-4ppm. Your pool’s pH level can be allowed to rise to between 7.8 and 8.0, so very little pH minus is required.

Shock Treatment

Maintaining a constant chlorine dose will help kill viruses, bacteria and algae but once a week it is important to boost the chlorine level to help prevent any of these problems occurring. This is known as a 'shock treatment'. You can use one of two chemicals for shock dosing.

Calcium Hypochlorite

Calcium hypochlorite is an unstabilised form of chlorine and is the most common form of shock dosing. As your chlorine source is a stabilised form of chlorine the calcium hypochlorite will help maintain a balance in the stabiliser level. Even if your pool is clean and clear it is still advised that you shock dose your pool once a fortnight or once a week during warmer periods. However if your pool has algae established in it and the water is green then a shock dose is required immediately to clear it.

It is very difficult to give an exact amount of calcium hypochlorite required to clear a green pool but as a guide:

  • Bottom of 2 metre pool is visible: 500 grams per 10,000 gallons
  • Only 1 metre depth is visible: 1000 grams per 10,000 gallons
  • Can't see the bottom: 2500 grams per 10,000 gallons
  • Pool is a very dark green colour: 5000 grams per 10,000 gallons

The required amount of calcium hypochlorite should be dissolved into a bucket of warm water and then poured into your skimmer.

Please Note: DO NOT MIX WITH ANY STABILISED CHLORINE AS IT WILL EXPLODE! Please make sure your skimmer is free from all other types of chlorine before pouring it into the skimmer.

Stabilised Chlorine Granules

Stabilised chlorine granules can be used as a form of shock treatment on smaller pools that are emptied regularly. It is advised that stabilised chlorine granules are used as a shock treatment on above ground liner pools that are only up for the summer season. This keeps things simple and reduces the chances of the pool liner being bleached. They cannot be used on larger in ground pools due to the high cyanuric acid level that will result from using two forms of stabilised chlorine as both your chlorine source and your shock treatment. High levels of cyanuric acid will create 'chlorine lock' resulting in the chlorine becoming ineffective.

Oxy Shock

This is primarily used for spa shock treatment rather than for pools. However if you are maintaining a chlorine free pool then you should use oxy shock - please contact us for advice.

Video Guide - How to clear a green pool

Water Balancers

For your pool to be safe for use, you need to maintain a suitable water balance whenever it’s in use. Water balance is defined as a condition where the water is neither corrosive nor scale-forming. The major factors in determining water balance are the pH of your swimming pool, the total pool alkalinity and calcium hardness. The nature of your local water supply plays a significant role in water balance; this is discussed in our ownership guide to hard and soft water areas.

pH – what is pH balance in a pool?

Maintaining the correct pH level in your pool plays an important role in how effective the chlorine is. The pH scale runs from 0-14, with 7 being neutral. Anything above 7 is considered alkaline and anything less than 7 is considered acidic.

In the context of pool water, a pH of 7.2-7.4 is the required range. Anything above 7.6 (more alkaline) reduces the effectiveness of the chlorine and can therefore promote viruses and bacteria. Anything below 7.2 (more acidic) makes the water corrosive and uncomfortable to swim in, causing irritation to the bather's eyes and skin.

How to balance pH and alkalinity in a pool

Altering the pH balance of swimming pools tends to be a difficult procedure due to the effect the alkalinity level has on them. The ideal range for pool alkalinity is 80-160ppm. If this is not sustained, it will ultimately affect the pH level. If the pool alkalinity level is too low, then this will create 'pH bounce' - meaning the pH level will fluctuate. If the pool alkalinity level is too high, then this will create 'pH lock' - meaning any alterations will not affect the pH level and the results will become inaccurate.

With that predicament in mind, it’s important to make sure the alkalinity level of your pool is correct before any pH alterations are carried out. After the correct alkalinity level is established, test the pH level of the water. If the pH level needs increasing further, add sodium carbonate (pH plus) and, if it needs decreasing, add sodium bisulphate (pH minus).

User tip: stating an accurate dosing amount can often be difficult due to the different natures of water supplies around the UK. The correct level required for your pool will become evident after a few doses but, as a general guide, dissolve 500 grams for every 10,000 gallons in a bucket of warm water and distribute around the pool. Leave the filter pump running for 24 hours and then re-test.

Pool alkalinity

As we’ve just established, the alkalinity level in your pool influences the pH level of water, so it’s vital that the alkalinity level is kept within the range of 80-160ppm to help keep the pH of your water correct. As such, reducing or increasing the alkalinity of your pool as per your requirements represents a vital part of maintaining pool water.

How to reduce alkalinity in a pool

If the alkalinity level is too high, then this can lead to scale forming on the fixtures and fittings. Pool alkalinity can be reduced using sodium bisulphate (pH Reducer). As with adjusting pH level, it’s hard to estimate exactly how much pH reducer a specific pool requires to reduce its alkalinity level to the appropriate range, therefore this process should be done a bit at a time to get used to how much is needed for your local water supply.

How to increase alkalinity in a pool

If the alkalinity level is too low, then the water can become corrosive and uncomfortable to bathe in. The corrosion can also damage the heaters and pipe work, resulting in them ultimately failing. Pool alkalinity can be increased using sodium bicarbonate (alkalinity builder).

User tip: 1kg of alkalinity builder increases the alkalinity level of a 10,000 gallon pool by 12ppm. This can be added directly to the pool and dissolved using a pool brush.

Calcium hardness – what does calcium hardness do to a pool?

Calcium levels are usually a factor in tiled pools. If you have a tiled pool and live in a soft water area, it’s important that you keep sufficient calcium in the pool water. This is not a problem in hard water areas, as the water supply will naturally contain enough calcium.

If there is insufficient calcium in the water of a tiled pool, the water will, over time, dissolve the calcium in the grout, making it soft. Eventually, the grout will disappear, leaving sharp edges which pose a cut risk to bathers. In a tiled pool, the calcium hardness should be kept above 200ppm. Calcium hardness can be increased by adding calcium chloride (calcium builder).

User tip: 1kg of calcium builder increases the calcium level of a 10,000 gallon pool by 12ppm.


Algae are a major problem for outdoor pools. A product of low chlorine levels, poor water balance or bad filtration (or a combination of any of the three), algae, particularly if left to develop and bloom, present a number of issues for pool owners. These include potential damage to the pool, making the water unsafe for use and changing the water colour to an unpleasant aesthetic.

With typical chlorine doses incapable of killing build-ups of algae, the only effective way to remove algae is by shocking the pool (see above). To avoid what is an unnecessary and time- and cost-consuming exercise, your best course of action is to prevent algae from occurring in the first place - which can be achieved by adding algaecide to your pool.

When to add algaecide to a pool

Algaecide is a chemical that both kills algal matter and prevents it from growing in the first place. It’s best utilised alongside a chlorine sanitiser as an effective tandem for keeping your pool clean. Using algaecide in your pool is recommended as part of your start-up process each season but also whenever your pool shows signs of developing or established algae.

Our most popular algae treatment, polyquat algaecide, is absorbed by organic debris such as leaves and dead algae, so it‘s important to clean the pool thoroughly with a brush or vacuum cleaner before starting the chemical treatment.

User tip: At the start of each season, it’s recommended to dose 1 litre of algaecide to each 10,000 gallons of pool water. This will help prevent algae getting established in your pool. Each week, add 100 millilitres to each 10,000 gallons of pool water to continue the protection against algae.

As well as using algaecide in your pool, there are also a few other things you can do to help prevent algae build-up:

  1. Brush regularly, especially the pool walls and deep end, to prevent invisible algae colonies from forming.
  2. Test your pool's sanitiser levels regularly and NEVER let sanitiser levels get low.
  3. Make sure your filter is working properly and that your pump runs at least 6 hours per day - preferably divided into two different intervals.

User tip: If you’re using our multifunctional tablets which already contain algaecide, you should only dose your pool with 1 litre of algaecide for every 10,000 gallons of pool water at the start of each season. After that initial dose, the multifunctional tablets will supply sufficient algaecide to help prevent algae from getting established.


What is flocculation?

In water treatment, the process of flocculation is the process of making small particles suspended in the water stick together to form clumps that can more easily be filtered out or settle to the bottom the pool where they can be vacuumed to waste. Flocculants are substances which improve the efficiency of your sand filter and help keep your water clearer. They release a coagulant to help remove fine particles which could otherwise pass through the filter and make the water cloudy.

How to use flocculant in your swimming pool

There are two forms of flocculant you can use on your pool:

Granular flocculant (aluminium sulphate)

Aluminium sulphate is added to the skimmer basket after backwashing to put a gel-like coat on the filter. This enables it to filter out particles which would normally pass through it.

User tip: backwash the filter before starting. Place 60 grams of aluminium sulphate for every 45 cubic metres (10,000 gallons) of pool water in the skimmer or strainer basket. The pool filter should be run continuously for at least 48 hours and only backwashed during this time if the pressure rises to the level recommended for backwashing. In the event of backwashing, repeat the dose.

Sparkle water clarifier

Sparkle water clarifier liquid flocculant directly flocculates the fine particles in the water, making them stick together in clumps so that they can be filtered out. The amount of sparkle water clarifier required is determined by how cloudy the water is – for example, the cloudier the water, the more sparkle you need.

User tip: To clear cloudy water, add 300ml per 45 cubic metres (10,000 gallons) of pool water. Dilute in a plastic bucket and distribute evenly around the pool with the filter operating. For routine use, add 60ml per 45 cubic metres (10,000 gallons) of pool water weekly. Please note that if you are using multifunctional tablets as your source of chlorine then these already contain a flocculant. Therefore, a weekly dose of flocculant is not necessary.

Swimming Pool Dechlorinator

Sometimes, too much chlorine gets into the pool - often by accidentally overdosing the water with chlorine or after a shock dosing to get rid of algae. High chlorine levels in a pool can pose a risk to bathers - and it’s not recommended to swim in water with more than 3ppm chlorine.

How to dechlorinate water

Our chlorine remover (sodium thiosulphate) is an effective dechlorinator for pools that will remove excess chlorine quickly and efficiently, to the point that you can swim again virtually straight after the process is completed.

Be careful not to overdose the chlorine remover, or you’ll have to once again reverse the process and add chlorine to get the water to a suitable chlorine level – which will mean unnecessary labour and cost to you.

As a general rule, 2 litres of swimming pool dechlorinator per 10,000 gallons of pool water will reduce the chlorine level by 5ppm.

User tip: Approach the process with caution. Underdose rather than overdose.

Testing your Pool Water


Method of Testing: Balanced Water Test Kit or Test Strips.
Ideal Range: 1-3 ppm
Reason for Testing: Testing the chlorine level in your pool is essential to ensure that you have enough chlorine and to prevent overdosing. If you are using chlorine as your main sanitiser it is very important to maintain enough chorine in your pool to kill bacteria and viruses, hence protecting the bathers. When boosting the chlorine level to eliminate algae it is necessary to allow the chlorine level to come down to its required rate before using the pool. A test should be done every time you use your pool, or each day during hot periods to reduce the chances of algae occurring.


Method of Testing: Balanced Water Test Kit or Test Strips.
Ideal Range: 7.2 - 7.4
Reason for Testing: To allow Chlorine to work to its full potential and to prevent any corrosion or scale forming it is important to maintain a pH within the ideal range. The correct pH level also provides comfortable bathing conditions for the bather as it reduces the chances of irritation occurring.


Method of Testing: Balanced Water Test Kit, Test Strips or Alkalinity Tablets
Ideal Range: 80-120 ppm
Reason for Testing: Maintaining the correct level of alkalinity in your pool helps prevent unwanted changes in the pH levels. If the alkalinity level is too low then the smallest amount of chemical treatment will alter the pH. If the alkalinity level is too high (over 180ppm) then it becomes very difficult to alter the pH. A level greater than 80ppm stabilises the pH of the water so that any chemical treatments or environmental factors will not rapidly alter the pH.

Calcium Hardness

Method of Testing: Balanced Water Test Kit, Test Strips or Calcium Hardness Tablets
Ideal Range: 100 ppm minimum
Reason for Testing: Calcium hardness is usually a problem for tiled pools in soft water areas. This is due to there not being enough calcium in the water so it will dissolve the calcium in the grout making it soft. In general this is not a problem in hard water areas as the water contains sufficient calcium.

Above Ground Pools

If you have an above ground pool that you are just using for the season it is advised to test the water each day using test strips. This is because it is a quick and easy way to keep on top of the chlorine level, which is vital during hot periods and high bather loads. These test strips also test for pH, alkalinity and hardness therefore covering every test you possibly need on an above ground pool.

Maintain your pool with the help of

Now you know how to maintain your home pool properly, it’s time to get started. All of the products you’ve read about above are available right here at – either click on the links highlighted in this guide or browse our site to find the individual products you need. You can also find a variety of starter and maintenance chemical kits that combine all the chemicals you need for particular pool and seasonal start-ups at a fantastic price.

Need some help with your pool maintenance or finding the right chemicals for your needs? Contact our team – we’ll be happy to help point you in the right direction.