This blog is about swimming pools, spas and hot tubs and how to maintain them.

Cow rescued from swimming pool

We recently came across this interesting article on the BBC.

A cow had to be rescued by firefighters from a swimming pool in Cheshire after falling through a pool cover after it mistook it for a solid surface. Firefighters had to pump out water from the pool before using bales of hay to create steps, which allowed the cow to get out of the pool and return to the safety of dry land.

Winterising your pool


With the school holidays over and autumn on the horizon, many pool owners will start thinking about closing their swimming pool down for the winter. This procedure is very important for two reasons. Firstly it helps ensure your pool is in the best condition possible when you come to open it up again in the spring and secondly it helps protect your pool and its fittings from the winter conditions. You can close your pool down by following the simple steps below.

  1. Backwash the filter and clean the strainer.
  2. Check the pH is between 7.2 and 7.6 and use sodium bisulphate (to lower pH) and sodium carbonate (to increase the pH) to adjust if necessary.
  3. Using Chlorine Shock (calcium hypochlorite), boost the chlorine level to remove any algae that maybe present in the pool. The recommended dosing rate is 1kg per 10,000 gallons of pool water.
  4. To prevent algae from growing add Winterising Algaecide. The recommended dosing rate is 2.5 litres per 10,000 gallons of pool water.
  5. Turn on the circulation to disperse the solution through the water for a period of 24 hours.
  6. Reduce the water level to just below the skimmers. This is to allow for any extra water that enters the pool, ie rainfall, therefore preventing it from overflowing. WARNING: Do not lower the level too much especially if the water table is high as this could cause structural damage to the pool shell.
  7. To protect any exposed metal surfaces, drain the water from the pump(s), filter(s), heater and pipework.
  8. Leave any valves above the water level open. Any below should be closed to protect from frost damage.
  9. Switch off the electricity supply to the system.
  10. Cover the pool with a heavy-duty winter pool cover.
  11. Check the appearance of the water, and the chlorine/pH levels occasionally during the winter.

By following this set of guidelines it should significantly reduce the amount of work you have to do when opening the pool up in the spring. Winterising Kits are available from our website which include all the chemicals you need as well as step-by-step instructions.

Please note the information provided on this page is believed to be correct but is given without warranty and no liability is accepted or implied. Please use this information in conjunction with manufacturers instructions.

What is calcium hardness?

When dealing with pool water the term ‘hardness’ can be somewhat confusing! Obviously water cannot be hard in a conventional sense unless it is frozen, so what does it mean and how does it affect the running of a swimming pool? Put simply hardness is the concentration of calcium and magnesium salts in the water. For the purpose of swimming pools we shall only deal with calcium in this post.

A rough guide to water supplies in the UK.

The water supply to our homes is often described as hard or soft.

Hard water

Hard water occurs due to the water supply filtering through soluble rock such as limestone and chalk, resulting in mineral salts like calcium dissolving into it. Water supplies in the south east of England are normally hard and this can lead to scale appearing on kettles and pool equipment. Hard water also stops your soap foaming as well. The main chemical which makes water hard is calcium bicarbonate. The calcium part is the hardness whilst the bicarbonate is the alkalinity. As a result hard water has a very high pH level.

Soft water

Soft water has very little minerals in it and as a result is very hungry to dissolve metals such as lead as well as concrete or grout in pools. To stop this from happening you will need to add calcium to the water which is discussed in more detail later on in this post.

Calcium hardness

Calcium hardness is a measure of the amount of calcium dissolved in water.

Why is calcium hardness important in swimming pools?

Most swimming pools are made of concrete and are often tiled with grout between the tiles. Pool equipment, particularly pumps and heaters are made of metal. As mentioned earlier soft water is hungry to dissolve anything soluble it comes into contact with so it will dissolve the concrete, grout and metals until it is satisfied. Therefore it is necessary to add calcium to the water to prevent this from happening.

What should the calcium hardness level be?

The ideal water for swimming pools is medium to hard water. The PWTAG publication “Swimming Pool Water – Treatment and Quality Standards for Pools and Spas” recommends the following concentrations of calcium in pool water:

  • Minimum 80 ppm
  • Maximum 150 ppm

Pools in hard water areas have over 200 ppm of calcium in the water supply so they will never have to add calcium. Pools that chlorinate using calcium hypochlorite will usually operate with calcium concentrations well over 150 ppm. This will not do any harm in a swimming pool unless it is very high (over 500 ppm).

PLEASE NOTE – These levels apply to swimming pools they do not apply to domestic hot tubs. Water hardness in hot tubs is discussed in a separate blog post.

The loss of grout on swimming pools is often blamed on low concentrations of calcium hardness in the water. Pool builders often recommend boosting the calcium hardness level to as high as 400 ppm to prevent grout loss. PWTAG carried out research on this and could find no evidence to support using a higher concentration of calcium hardness.

How to adjust calcium hardness

To increase the calcium level you need to add calcium builder (calcium chloride) or use calcium hypochlorite as your source of chlorine.

1.5kg of calcium chloride will increase the calcium hardness level by approximately 20ppm in a 10,000 gallon (45m3) pool.

In a soft water area the calcium level can be decreased by diluting with mains water (backwashing). In hard water areas the only way of decreasing the calcium level is to use a water softener which is not recommended or necessary in swimming pools.

How to test for calcium hardness

Calcium hardness can be tested using test strips, a comparator, a photometer or the traditional tablet counting method, which in my opinion is more accurate than either of the aforementioned methods.

Please note once you have established that your water supply is hard, you rarely need to check the calcium hardness level.

Tablet Count Testing Method:

  1. Fill a dilution tube with 100ml of pool water.
  2. Add calcium hardness tablets one at a time and shake the sample to ensure they are dissolved.
  3. When the water changes colour from pink to bright purple the test is complete.
  4. The calcium level is obtained by the following formula; (the number of tablets used  x 20 ) – 10

For example if 7 tablets are used the calcium level is (7 x 20) – 10 =  130 ppm


Looking after your pool in the rain


With all the rain around recently the last thing you have probably felt like doing is going outside for a swim and who could blame you! However it is still important that you look after your pool so when the sun reappears it will be in top condition and ready for you to use.

The reason for this is because during spells of heavy rain the rain washes dust and algae spores into the pool and uses up the chlorine. When the chlorine disappears algae will start to thrive and before you know it you are faced with a horrible green swamp instead of a nice sparkling pool. So instead of enjoying a nice relaxing swim you are having to shock treat it with a lot of chlorine to try and get rid of all the algae.

It is therefore important to take pre-emptive action to prevent this by following these simple steps;

  • Give the pool a shock dose of 500grams  of calcium hypochlorite granules (shock chlorine) for every 10,000 gallons of pool water. You can use stabilised chlorine granules if you have an above ground pool.
  • Add an algaecide to your pool.
  • If you use stabilised chlorine tablets or multifunctional tablets put an extra tablet in the skimmer and run the pool at the high end of the chlorine range.

Even though you are unlikely to use your pool during bad weather, using some extra chemicals now will save you a lot of effort and chemicals in the medium term and it will allow you to use your pool when the good weather returns.

What is Stabiliser?


If you look at your test strips you may notice a pad that tests for stabiliser, but what is it and how does it effect the way you maintain your pool?

A stabiliser is added to the pool water to reduce chlorine loss due to ultraviolet light from the sun. It is usually added to the water via a chemical called cyanuric acid. “According to research results, pools without stabiliser lose about 90% of their total chlorine residual on a sunny day in two or three hours. Pools with 25-50ppm of cyanuric acid, however, under the same conditions, lose only 10 to 15 percent of their total chlorine.” (White et. al. , 1972)

You may not have heard of or even used cyanuric acid before as it is already included in the majority of chlorine products on the market. You may be familiar with chlorine based products such as Stabilised Chlorine Granules, Stabilised Chlorine Tablets or Multifunctional Tablets (a form of the stabilised chlorine tablet). All these products contain cyanuric acid which is why they are referred to as stabilised chlorine. Therefore as well as dosing chlorine into the water they also add cyanuric acid at the same time.

As mentioned earlier only a small amount of stabiliser (25ppm) is needed and the stabiliser level is acceptable up to a level of 100ppm. Once the level exceeds this amount the chlorine becomes less effective. If this happens then you have two choices. You can either switch to an unstabilised form of chlorine such as Calcium Hypochlorite or Sodium Hypochlorite until the stabiliser level drops, or you can replace a proportion of your water. If you choose the latter option then drain your pool by two thirds and replace with fresh water immediately. Do not wait to refill the pool as this could cause damage to the structure of your pool. Always check with your pool builder before emptying your pool.

Indoor pools

If you have an indoor pool that is not exposed too much sunlight, you should consider using an unstabilised form of chlorine such as Calcium Hypochlorite Tablets or Sodium Hypochlorite. There is no need to add cyanuric acid to an indoor pool and if you do the stabiliser level will build and eventually you will have to drain some of your water.

Pool Blaster Catfish Pool Cleaner


SP993MIf you are looking for a pool cleaner that is quick and convenient to use then look no further than the Pool Blaster Catfish from Water Tech.

The Catfish is totally independent from the main pool filtration system which means there is no need for any hoses, cables or additional pumps. It works off a rechargeable Nickel Metal Hydride battery which has a run time of 45 minutes when fully charged. It attaches to all standard telescopic poles making it suitable for all types of pools and spas. It has a 8″ vacuum head and a reusable filter bag which collects leaves, algae and even fine particles such as sand.

It is available for just £139.99 from our website.

Above Ground Pool Chemicals – Water Testing


This week we have taken you through all the major chemical parameters that you need to control on an above ground pool. Now we are going to take you through testing these parameters. Testing your pool water on a daily basis is crucial to provide a clean, safe and comfortable bathing environment for all bathers.

When testing the pool water you are testing for the following:


Reason for Testing: To ensure there is enough chorine in your pool to provide a safe swimming environment.
Recommended Level: 1-3ppm
Level too Low: Open the collar more on your floating dispenser or add stabilised chlorine granules
Level too High: Remove the floating dispenser from the pool and do not add any more chlorine. Remove the pool cover and chlorine will come down on its own.


Reason for Testing: To allow the chlorine to work to its full potential and provide comfortable bathing conditions for the bather.
Recommended Level: 7.2-7.6
Level too Low: Add pH Increaser
Level too High: Add pH Reducer

Other test parameters include Alkalinity and Stabiliser (Cyanuric Acid). The Alkalinity level is not very important on above ground pools but if you are experiencing low levels of alkalinity add a small amount of Alkalinity Builder. If your alkalinity level is too high then it can be reduced using the pH Reducer. As above ground pools are only up for the summer the stabiliser level will not reach a level that will cause concern. In the unlikely event that it does all you need to do is replace a portion of the pool water with fresh tap water.

How do I test for these?

When testing, it is important to have a testing method that is both accurate and reliable. For above ground pools a straightforward testing method such as test strips or a pool tester kit is more than sufficient.

Test Strips

730aTest strips are a popular method of testing the water in above ground pools due to the fact that they are quick and easy way to obtain accurate results. AquaChek test strips are renowned as one of the worldwide leaders in the test strip industry.

The general testing procedure is:

  • Dip your strip into your pool water and remove immediately.
  • Wait 15 seconds.
  • Compare the colour pads to the colour chart on the bottle.

Testing Tips

  • To get the best out of your test strips, store them in a low humidity environment at room temperature.
  • Keep wet fingers out of the bottle to enable accurate results when testing.
  • Do not use any test strips that are out of date.
  • Keep a record of your results, as they can be an excellent reference point when talking to dealers or professionals. They also help you to understand what is going on in your pool or spa.

Pool Tester Kits

An alternative way to test your pool is with a test kit. A test kit normally consists of a clear container split into two sections, one for chlorine and one for 714pH. Each section is filled with pool water and then a DPD 1 tablet is added to the chlorine section and a Phenol Red Tablet is added to the pH section. Once added the water will change colour and this is then compared to the colour chart on the front of the container to obtain your chlorine or pH level.

This week we have taken you through all the important points that you need to be aware of when maintaining an above ground pool. There are other chemicals that you may come across such as algaecide and flocculant and if you would like to find more out about these chemicals you can visit our guide for above ground pools.

Above Ground Pool Chemicals – pH


Day 4 of our guide to maintaining above ground pools looks at pH. Along with the chlorine level, pH plays an important role in providing a comfortable bathing environment in your pool. 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 7.2 – 7.6 is the recommended level to bathe in.

pH Scale

  • 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.

Altering the pH Level

To increase the pH level add pH Increaser
To reduce the pH level add pH Reducer

  • Dissolve 45g per 1,000 gallons in a bucket of pool water and distribute around the pool with the filter pump running.
  • Retest after 4 hours.

Tomorrow we will complete our guide to maintaining above ground pools with a look at water testing.

Above Ground Pool Chemicals – Shock Treatment


This week we are taking you through everything you need to know about maintaining an above ground pool this summer. Today we look at shock treatment.

A shock treatment is a boost of chlorine that should be done once a week during the summer or if the pool has problems with algae. You should also do a shock treatment if the pool has been used prior to adding any chemicals. If the pool is used a lot (during holiday periods) and is cloudy at the end of the day it is a good idea to shock it so that it can recover over night.

What should I use as a shock treatment?

For above ground pools it is recommended that you use Stabilised Chlorine Granules or Multi-5 Chlorine Granules as a form of shock treatment. The aim of the shock treatment is to increase the chlorine level by approximately 5ppm to kill any impurities in the water.

Shock Dosing Procedure

  • If you are using tablets and a dispenser remove these from your pool and place in a bucket.
  • Fill a clean plastic bucket with pool water and add the required amount of granules to the bucket. 50 grams will increase the chlorine level by 5ppm in a 1,000 gallon pool.
  • Once this has been thoroughly stirred, distribute it around the pool spreading it around as much as possible making sure it reaches all areas of the pool.
  • It is recommended that you don’t enter the pool until it has returned to its normal range (1-3ppm).

What do I do if my pool goes green?

If your pool goes green you have two choices.

A green pool.

  1. Empty and clean the pool before refilling and treating with chlorine.
  2. Shocking the pool with chlorine and filtering the dead algae out.

The amount of chlorine needed to clear a green pool depends on how green the pool is. However it is better to overdose a pool with chlorine to ensure all the algae is killed. If you do not use enough chlorine you will only kill a small amount of the algae and the remaining algae will multiply rapidly using the nutrients from the dead algae and you are back to square one. All pools are more prone to going green in adverse weather as algae spores and dirt are washed into the pool. To combat this, consider using a debris cover when it is raining.

A very green pool could need as much as 250grams per 1,000 gallons.

Top tips for shock treatment

  • Use stabilised chlorine granules or multi-5 chlorine granules.
  • Shock treat your pool once a week at a time when it is not likely to be used
  • Always dissolve any granular chemicals in a bucket of water before adding them to your water.
  • Always allow the chlorine level to return to 1-3ppm before returning to the water.

Tomorrow we will look at pH in above ground pools.

Above Ground Pool Chemicals – Chlorine


56996 10x10cmThis week we are taking you through everything you need to know when maintaining an above ground pool throughout the summer season. Yesterday we started by giving you a brief introduction into chemicals for above ground pools and today we are going to focus on the most important of those chemicals; chlorine. Chlorine is responsible for killing any bacteria or viruses that get into the water, therefore it is crucial that you treat your pool with chlorine and maintain the correct level of chlorine at all times (between 1 and 3 ppm).

Stabilised Chlorine is predominantly used on small above ground pools as it contains a stabiliser called cyanuric acid, which prevents the chlorine being broken down by the sunlight. There are several ways in which you can dose the stabilised chlorine into your pool water depending on what budget you have and how much work you would like to do.

Stabilised 20g Chlorine Tablets

The recommended way to dose your pool is with 20gram tablets and a floating dispenser. You can either use standard Stabilised 20g Chlorine Tablets or Multifunctional 20g Tablets, which contain an algaecide and a flocculant as well as the chlorine. This enhances the clarity of the water and also assists in preventing algae forming. By using any form of stabilised 20g chlorine tablet you have the peace of mind that you are providing a constant dose of chlorine at all times and hence reducing the amount of work you have to do in order to look after the pool.


Small Floating Dispenser

Dosing Stabilised 20g Chlorine Tablets or Multifunctional 20g Tablets

  • Fill the floating dispenser with tablets.
  • Fully open the blue ring at the bottom.
  • Place the dispenser in the pool and leave it to float around.
  • The rate of dissolution can be controlled by opening and closing the blue ring at the bottom.
  • When the pool is in the use the dispenser is taken out and put into a plastic container well away from the children.

As a general rule if your chlorine reading is towards the latter end of the scale (3ppm) then only have the blue ring open a little and if it is towards the lower end of the scale (1ppm) then open it up more.

Stabilised Chlorine Granules


Stabilised Chlorine Granules

If you are on a tight budget you can use stabilised chlorine granules (sodium dichloroisocyanurate) which is a granular form of chlorine that requires manually dosing. You can either use standard Stabilised Chlorine Granules or Multi-5 Chlorine Granules which contain an algaecide and a flocculant as well as the chlorine. This enhances the clarity of the water and also assists in preventing algae forming. Please note that if you are using Stabilised Chlorine Granules you will need to be more vigilant with the chlorine level to ensure it remains within the recommended range. You may also need to dose the pool regularly to cope with the demand for chlorine.

Dosing Stabilised Chlorine Granules or Multi-5 Chlorine Granules

  • Fill a clean plastic bucket with pool water and add the required amount of granules to the bucket.
  • Once this has been thoroughly stirred distribute it around the pool spreading it around as much as possible making sure it reaches all areas of the pool.

As a general rule 10 grams will increase the chlorine level by 1ppm in a 1,000 gallon pool.

Whichever method of dosing chlorine you use it is vital that you test the chlorine level regularly and maintain the correct level of chlorine in your pool (1-3ppm). We will look at testing your above ground pool in more detail later on this week, however the easiest way to test the chlorine level in your pool is by using a test strip.

Tomorrow we will look at shock treatment in above ground pools.