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

Preventative action after summer rain storms


After a good start to June the majority of the UK have been treated to heavy storms over the past week. This may have resulted in you forgetting about your pool, however this is often a mistake as pools can go off when there is rain following good weather. The rain washes dust and algae spores into the pool and the dirt uses up the chlorine, allowing  the algae to thrive in the very warm water. The water goes green and it then requires a lot of shocking with chorine and dosing of algaecide to get the pool back to its previous pristine condition. 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 thundery 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.

Video – How to clear a green pool


Want to know how to clear a green pool? Check this video out to see how to get your pool from green to clean!



What is a comparator test?


Comparator Test Kit with Disc

If you are looking for an alternative to test strips when it comes to analysing your pool or spa water then you might consider using a comparator test kit. A comparator is an item of testing equipment used to visually test pool water for parameters such as free chlorine, total chlorine, total bromine and pH. Usually they come in the form of a comparator disc and unit but there are more basic kits on the market that don’t have a disc and just have a colour scale on the side of the test tube.

To conduct a comparator test the first thing you need to do is rinse the test tubes out with tap water. This removes any traces of previous tests that could affect the result. You then need to take two 10ml samples of water. One will be used as a blank in the comparator unit and the other will be used to perform the test. You then need to add the reagent to the sample and crush it using a crushing rod. When doing this you will see that the sample changes colour (if you are doing a chlorine test then it will hopefully turn a shade of pink). Once the tablet has fully dissolved you need to hold the unit up to the light and look through the view finder on the comparator unit and turn the comparator disc until the two colours match. When you have achieved the closest match, read the relevant number off the disc to determine the level in the water.


Basic Comparator Test Kit

There are normally three tests you can do using a comparator and these are;

  • Free Chlorine or Bromine using a DPD 1 tablet.
  • Total Chlorine using a DPD 3 tablet.
  • pH using a phenol red tablet.

If you are using a basic comparator test kit then the process is similar but you don’t use a blank sample. Instead you fill the relevant compartment up with water, add the reagent and then compare the colour of the sample to the colour chart on the face of the compartment.


Opening your pool for the Spring?


As we move into March most pool owners across the country will start thinking about pulling back the pool cover and getting the pool ready for the spring. If you winterised the pool at the beginning of last winter then opening the pool should be a relatively straightforward process, but nevertheless here is a simple step-by-step guide on how to get your pool ready.

Preparing the Pool

  1. Remove any leaves and debris from the winter cover. Take the winter cover off, clean it and store it away.
  2. Connect the pool pump and filter and reconnect all hoses and electrical connections.
  3. Remove leaves and debris from skimmers, filters, pumps and drains.
  4. Remove any debris and leaves that are in the pool using a leaf skimmer.
  5. Fill the water up to the proper water level. The water should be halfway up the skimmer opening.
  6. Turn on the filter pump and make sure all skimmers, bottom drains and filters are functioning properly.

Adjusting the pH and Alkalinity Levels

  1. After the pool filter has been running for 3-4 hours, test the pH and alkalinity levels and compare with the table below.
  2. To reduce the pH level use pH Reducer. Dissolve a small amount (450g per 10,000 gallons) in a bucket of pool water and distribute it around the pool with the filter operating. Retest after 4 hours.
  3. To increase the pH level first adjust the Alkalinity to between 60-100ppm. To increase the Alkalinity level by 12ppm add 1kg Alkalinity Builder per 10,000 gallons directly to the pool with the filter operating. Retest the Alkalinity level and the pH level after 4 hours.
  4. If the pH level is still too low dissolve a small amount (450g per 10,000 gallons) of pH Increaser in a bucket of pool water and distribute it around the pool with the filter operating. Retest after 4 hours. Repeat this dosage if necessary.
Low OK Ideal OK High
pH Less than 7.0 7.0-7.2 7.2-7.6 7.6-7.8 Over 7.8
Total Alkalinity Less than 40ppm 40-60ppm 60-100ppm 100-120ppm Over 120ppm

Shock Treat the Pool

  1. Brush the pool walls and steps and vacuum up any debris. This will expose the algae to the chlorine.
  2. Dissolve 500 grams per 10,000 gallons of Chlorine Shock in a bucket of pool water and distribute around the pool. DO NOT ADD TO THE SKIMMER BASKET IF IT HAS HAD STABILISED CHLORINE IN IT AS IT MAY EXPLODE IF MIXED!!!
  3. Depending on how green the pool is it might require several shock treatments. If your pool is very green you can double the initial shock dose. Following the shock dose, backwash the filter to remove any debris.

Stabilising the Chlorine Level

  1. After a few days your chlorine level should have returned to normal (see table). Once it has you can now add a 200g Multifunctional tablet or 200g Stabilised Chlorine tablet to your skimmer basket or dispenser.
  2. To improve the clarity of the water add Sparkle Water Clarifier to a bucket of pool water and distribute around the pool.
  3. To prevent algae re-occurring add Polyquat Algaecide to a bucket of pool water and distribute around the pool.
Low OK Ideal OK High
Chlorine Less than 0.5ppm 0.5-1.0ppm 1.0-3.0ppm 3.0-5.0ppm Over 5.0ppm

Daily Maintenance

  • Monitor Chlorine, pH and Alkalinity levels using AquaChek Free Chlorine Test Strips.

Weekly Maintenance

  • Clean the skimmer baskets and brush the walls, steps and bottom of the pool. Vacuum if necessary.
  • Clean the strainer basket before the pump. When this is complete backwash the filter.
  • Shock dose the pool. Dissolve the required amount (see instructions) of Chlorine Shock in a bucket of pool water and distribute around the pool. DO NOT ADD TO THE SKIMMER BASKET IF IT HAS HAD STABILISED CHLORINE IN IT AS IT MAY EXPLODE IF MIXED!!!
  • Add Sparkle Water Clarifier to a bucket of pool water and distribute around the pool.
  • Add Polyquat Algaecide to a bucket of pool water and distribute around the pool.

Dosing Information – Health and Safety

  • Always wash out the container you mix chemicals in thoroughly with pool water before and after use.
  • Do not ever mix chemicals together
  • Always add chemicals to water not water to chemicals.

Calcium Hypochlorite Granules (Chlorine Shock)


Calcium Hypochlorite (Chlorine Shock) is an unstabilised form of granular chlorine that is most commonly used as a shock treatment in swimming pools. It has 70% available chlorine which makes it stronger than other shock treatment chemicals such as Sodium Hypochlorite (14-15%) and Stabilised Chlorine Granules (56%). Another major advantage of using calcium hypochlorite as a shock treatment is that it doesn’t contain any stabiliser. There can be occasions where you need to add a large shock dose in order to kill algae. If  you used a stabilised chlorine like the aforementioned Stabilised Chlorine Granules, then it would still kill the algae but it would also increase the stabiliser level in the water. Over time the stabiliser level will build up  and eventually it will get too high and you will have to reduce it by draining a proportion of pool water and replacing with fresh water.

Calcium hypochlorite granules should be dissolved in a bucket of warm water and distributed around the pool or poured into the skimmer basket. HOWEVER please make sure your skimmer basket is free from all other types of chlorine before pouring it in. The reason for this is if you mix unstabilised chlorine and stabilised chlorine together in their raw form they will react violently. Once they are added to the pool separately they are fine. People often use a trichlor tablet as their sanitiser and calcium hypochlorite granules as their shock treatment. If this is the case put the trichlor tablet in the skimmer basket and when it is time for a shock treatment, dissolve the calcium hypochlorite granules in a bucket of warm water and pour the solution around the pool. This will ensure you keep the two types of chlorine separate from one another.

It is not recommended to use calcium hypochlorite granules in a spa as it is undesirable to have large amounts of calcium build up in a spa. It will cause scaling of the heater and white deposits on the sides therefore we recommend using Oxy Shock instead.

How does your water supply affect your Hot Tub maintenance?


Did you know that your water supply plays a significant role in how you go about maintaining your hot tub water? The water supply in our homes is usually referred to as hard or soft and it is important to know your water supply as it will affect some aspects of your hot tub maintenance.

A quick way to determine whether you have hard or soft water is to take a quick look in your kettle. If you can see signs of scale then your water supply will be classed as hard. If you can’t then it is likely to be soft. If you are unsure you are best to check with your local water board.

If you live in a hard water area then you need to be aware of two main issues; scale and a high pH level. I mentioned earlier about the build up of scale in your kettle. The chances are it will be a similar picture on the internal pipe work and heater in your hot tub. If left untreated then this could eventually cause significant damage, especially to the heater. With this in mind it is important that you use a scale inhibitor such as our Stain and Scale Inhibitor.

The main chemical that makes water hard is calcium bicarbonate. The calcium part is the hardness whilst the bicarbonate is the alkalinity. As a result the second problem you will probably encounter is a high pH level and high alkalinity level. Both of these issues can be rectified by adding a pH Reducer, which is usually sodium bisulphate. If you do live in a hard water area it may be prudent to run your hot tub on bromine as you can maintain a pH level between 7.2 and 8.2. If you run on chlorine then you must maintain a pH level between 7.2-7.6.

If you live in a soft water area then the opposite will happen as your water supply will have a low pH level and low alkalinity level. First of all you need to get your alkalinity level right and you can do this by adding an alkalinity builder, which is sodium bicarbonate. Once you have added this you will find that it slowly also brings your pH level into the desired range.

Trick or Treat?


With Halloween fast approaching we thought we would share some pool and spa tricks with you that will hopefully help you when maintaining your pool or spa.

  1. If you have an indoor pool, consider using unstabilised chlorine instead of stabilised chlorine. This will prevent the stabiliser level from getting too high and prevent the need to dump any water.
  2. When dosing granular chlorine always dissolve the required amount of chlorine into a bucket of water before adding it to the pool. This will ensure that no chlorine goes to waste and also prevent any bleaching of the pool liner.
  3. When altering the pH level always ensure the alkalinity level is correct first as this has an effect on the pH.
  4. If you have a green pool you may need to double or even treble the normal shock dose in order to kill the algae. As there is no way of measuring algae it can be difficult to give an exact amount but always overdose rather than under dose or else you could end up going round in circles!
  5. When buying Chlorine Shock just purchase enough for one season. Due to the nature of the chemical if it is kept in storage for too long it can start to attack the packaging, making it brittle and weak.
  6. Over the winter in addition to winterising your pool, keep a large floating dispenser in your pool with a 200g Multifunctional Tablet in it. This will further enhance the condition of your pool when you open it up again in the spring.
  7. After refilling your spa or hot tub, use either Bromine Spa Starter or Chlorine Granules to quickly establish a bromine/chlorine level. If you only use tablets it will take a while for you to establish a suitable sanitiser level in your spa.
  8. Use Oxy Shock to shock treat your spa as it is faster dissolving than chlorine shock and it fully dissolves. Also it doesn’t produce the chlorine smells you get with a chlorine based shock.
  9. To improve the clarity of your water, shower before using the spa. This will get rid of any lotions and perspiration that would normally cloud the water.
  10. Drain and refill your spa on a regular basis. As a rough guide a 1000 litre spa should be drained after 100 bathers.


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