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

Sea lion takes a dip in public swimming pool


This article caught our eye in the Daily Mail on Monday. Swimmers at an open-air public swimming pool in Dunedin, New Zealand were given a surprise recently when an unexpected guest turned up. At around 2.30pm holidaymakers and locals were joined in the pool by a sea lion who had casually made its way past reception and cafe before taking the plunge into the saltwater pool. Although New Zealand sea lions are known not to fear humans, swimmers quickly evacuated the pool and after a nice leisurely swim, the sea lion made its way out of the pool and back to its normal surroundings.

Hot Tub Starter Kits


Happy New Year to you all!

If you are thinking of purchasing a hot tub, shortly after installing it you will need to purchase some chemicals in order to keep the water safe to bathe in. If you are not experienced in maintaining a hot tub it can be daunting when faced with all the different chemicals. What are they? What do they do? How much do I need? These are probably just a few of the questions running through your mind. However, there is a simple answer to all these questions. Buy a chemical starter kit!!

Starter kits offer a cost effective and hassle-free method for ensuring you get your hot tub up and running and safe to bathe in. The basic starter kits on the market will contain chlorine (or bromine), a shock treatment, water balance chemicals and some test strips. These are the essential chemicals that you need to get your hot tub started. However, it is important to note that when maintaining a hot tub the likelihood is that you will need to use additional chemicals in the future, such as a water clarifier, filter cleaner, antifoam and perhaps a scale inhibitor if you live in a hard water area. It is therefore advisable to purchase a starter kit that also contains these additional chemicals. It may be more expensive at the start but you will save money in the future. Also if you do encounter any problems, such as foaming, you will have the peace of mind of knowing that a short trip to the garage or shed will sort the problem out quickly.

All good starter kits should also come with an instruction leaflet on how to run a hot tub. These are often quite extensive and provide a great deal of valuable information. This will help to ensure that maintaining your hot tub is a hassle-free experience.

We have a range of hot tub starter kits on our website, all of which include clear instructions on starting and maintaining your hot tub. Please click here for more information. If you are unsure on whether to use chlorine or bromine then please read our relevant blog post on this subject.

Chlorine or Bromine in a Hot Tub?


One of the most common questions we get asked from spa and hot tub owners is which is the best sanitiser to use – Chlorine or Bromine? There are many theories out there as to which is better, however we decided to gain firsthand experience and run our test hot tub on both in order to provide you with a practical answer. The conclusion we came to is that both are perfectly suitable sanitisers, however bromine does boast three crucial advantages over chlorine, which we believe makes it a more suitable sanitiser for hot tubs.

Less odorous – Running your spa on chlorine can create a strong chlorine smell in the water even when the chlorine level is kept within the recommended range of 2-4 ppm. Although this is perfectly normal it can result in an unpleasant bathing experience. Bromine is less odorous than chlorine and as a result this smell doesn’t exist and a more pleasant bathing environment can be enjoyed.

Effective at a broader pH range – The recommended pH level for a chlorine spa is 7.2 – 7.6. This is because the effectiveness of the chlorine as a sanitiser significantly decreases at higher pH levels. Bromine on the other hand, is an active santiser at pH levels of 8.2, therefore the pH level can be maintained at a much broader range of 7.2-8.2. This allows more flexibility when controlling the pH level and is particularly beneficial for hard water areas where the incoming water supply naturally contains high pH and alkalinity levels.

Slower dissolving – Regardless of which sanitiser you use, both are available in tablet form and ideally should be used in conjunction with a floating dispenser. The main difference we experienced is that bromine is much slower dissolving than chlorine and as a result it is a lot easier to maintain the correct sanitiser level in the water. This is crucial in order to reduce the amount of work involved in maintaining your hot tub.

To make this a fair argument it is only right that we look into the disadvantages of using bromine over chlorine. As bromine is slow dissolving it can have difficulty in recovering an adequate concentration after the hot tub has been heavily used or is started up after being emptied. In this case you need to add another sanitiser such as oxy shock or stabilised chlorine granules just to boost the level. Another disadvantage is price, as bromine is a little more expensive than chlorine.

Despite these drawbacks we firmly believe that the advantages of using bromine over chlorine far outweigh the disadvantages. As a result we would always recommend using bromine as opposed to chlorine in a hot tub.

Emptying a spa or hot tub


Even though your spa water is continuously re-circulated, treated and filtered, not all the pollution added by bathers to the spa will be removed. With this in mind it is important to drain and refill your spa on a regular basis. There are no set rules as to when you should do this however it is recommended that the water be changed after 100 bathers per 1000 litres of spa water. For example a 1500 litre spa would need to be drained after 150 bathers. If there are 2 bathers a day then it would need to be changed after 75 days.

Regardless of how many bathers use the spa the water should be changed at least every 3 months. This is a good opportunity to give the spa a good clean before starting the start-up procedure again! Before you empty the spa we recommend adding some spa and hot tub pipe cleaner to the water. Add 250ml per 1000 litres of spa water, directly to your spa and run the jets for one hour. Drain and rinse the spa thoroughly.

Closing your pool for winter


Now we have entered September 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.

Removing chlorine from a pool


Dechlorinator is a sodium thiosulphate solution that allows you to safely remove chlorine from your pool should accidental over-chlorination occur. It isn’t recommended to swim in water that contains more than 3ppm of chlorine however you shouldn’t use Dechlorinator unless the chlorine level goes above 10ppm. If your chlorine level is between 3 and 10ppm it is recommended that you stop dosing your pool with chlorine and allow the chlorine level to come down naturally over time. The reason for this is if you put too much dechlorinator into the pool then you will need to add a lot of chlorine to establish a chlorine level again. This is good for chemical suppliers profits but not for your pockets!!!

Before you add any dechlorinator it is important that you ascertain an accurate chlorine reading. This may involve doing a dilution test if the chlorine is bleaching out your test reagent. Once you have an accurate chlorine reading, pour the required amount of dechlorinator into a bucket of water and then distribute evenly around the pool. Allow the pool water to turnover twice before testing the pool water again.

Shock Treating an Above Ground Pool


With the UK currently experiencing a heat wave and the school holidays upon us, many children (and adults!) will be enjoying their above ground pool. Ensuring the water in the pool is safe to bathe in is of paramount importance and one of the crucial procedures involved in this process is shock treating the pool water.

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.

You can also see our video on shocking an above ground pool in one of our previous blogs.

Chlorine for Above Ground Pools


56996 10x10cmOne of the most frequently asked questions we receive is “What type of chlorine should I use in my above ground pool?”

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.

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

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.

From green to clean!


With the sun making a welcome appearance recently many pool owners across the UK have removed the cover off their pool and started to get their pool ready for the summer. One of the most common problems we hear about at this time of year is a green swimming pool due to algae growth. Getting it back to its sparkling best may seem like a daunting task but if you follow these guidelines you will soon have your pool looking crystal clear again.

The most effective way of killing the algae is to boost the chlorine level in the water by adding a shock dose of chlorine. The chemical most commonly used for this in in-ground pools is calcium hypochlorite granules (shock granules). In above ground pools which are emptied every year or two stabilised chlorine granules can be used. NEVER MIX CALCIUM HYPOCHLORITE AND STABILISED CHLORINE GRANULES AS THEY CAN EXPLODE!!

The amount of shock granules you will require depends on how much algae is in the water, however this is very hard to measure. In the process of killing the algae the chlorine is used up. It appears that you are adding chlorine and it is just disappearing. The dead algae break down in the water and have the potential to be food for any still alive. Therefore to get rid of the algae completely sufficient chlorine has to be added to kill the entire population in the pool and establish a level of chlorine in the water; otherwise the algae carries on breeding in the pool so the chlorine seems to be having no effect. For this reason for pools which are very green the pool may have to be shocked several times.

As a rough guide:

  • The normal shock dose is 500 grams per 10,000 gallons of pool water. This is sufficient to clear a pool which is slightly green (objects on the bottom of a 2 metre deep pool are visible).
  • If you can only just see the bottom in 1 metre of water add 1000 grams per 10,000 gallons.
  • If you can’t see the bottom, add 2500 grams per 10,000 gallons (Pool A).
  • If the water looks like pea soup add 5000 grams per 10,000 gallons (Pool B).

Pool A

Pool B









In each case put about 8 litres of luke warm water in a plastic bucket and dissolve 500 grams of calcium hypochlorite (shock granules ). Mix well. Calcium hypochlorite does not dissolve completely so you will get a milky suspension. REMEMBER always add chemical to water NOT water to chemical. Ideally this solution should be added slowly into a skimmer, with the circulation pump running, so that it will get well mixed throughout the pool water. BEWARE DO NOT PUT CALCIUM HYPOCHLORITE INTO A SKIMMER THAT HAS EVEN A TRACE OF ANY STABILISED CHLORINE IN IT AS THEY REACT EXPLOSIVELY.

Repeat this process until you have added the required amount of chlorine or the algae turns to a lightish colour. If you cannot add to a skimmer try spreading the solution through the pool as evenly as possible using a plastic watering can.

Allow the pool to circulate for at least 2 hours. Check the chlorine level. It should be above 5 ppm but may be very high. If the chlorine level is low and the algae is still green add another shock dose (500 gram per 10,000 gallons).

If your pool was very green it will now be cloudy due to dead algae. The dead algae has to be filtered out so it is best to add 250 mls. of sparkle water clarifier per 10,000 gallons and run the filter continuously. Some of the dead algae will drop to the bottom of the pool which will need to be vacuumed out.

Just shocking the pool is unlikely to get rid of algae growing on the pool sides and bottom. This algae will need to be physically removed by scrubbing and then shocking the pool as described above. If your pool is a tiled or concrete pool and the algae is growing in the grout you can sprinkle some shock granules into the pool allowing them to sink to the bottom and then brush the granules over the algae. In severe cases you may need to scrub with an algae brush.

Do not allow shock chlorine to stay on the bottom of a liner pool as prolonged contact may discolour the liner.

When you have cleared the algae add 1 litre of polyquat algaecide per 10,000 gallons Or switch to multifunctional tablets which contain an algaecide and flocculant.

Flooding of Outdoor Pools


Now the weather is improving a little, thoughts are turning to the opening and re-commissioning of outdoor pools, both domestic and the few public ones. Everywhere the water table will be high and some liner pools will be floating. Pools cannot therefore be drained and so chemical cleansing will have to be done, more than ever.

One thing that causes concern is the flooded pools, many of which are already green with algae because of the mild winter and may well have all sorts of sewage and field run off in them. It would be a wise precaution to carry out super-chlorination of all pools in advance of their use by bathers so as to try and inactivate any cryptosporidium that may be present.

It would be appropriate to dose at 20 mg/l for at least 13 hours with the pump and filter running.  The quantity of chlorine required will depend on how much dirt is in the water. The quantity of shock chlorine (calcium hypochlorite) required is likely to be at least 3kg per 10,000 gals or if using sodium hypochlorite 15 litre per 10,000 gals. There should be no problem in using these quantities of chemicals in a tiled pool, but if it is a liner pool, check with the liner manufacturer and take particular care with older liner pools.  Please note that in theory, it is possible to reduce the concentration to say 10 mg/l and double the contact time.  However, it is best to use maximum chlorine concentration to inactivate cryptosporidium.

It is important to check the free chlorine residual (DPD1) every few hours (using dilution method to avoid any bleaching out). It may be necessary to add more chlorine for very dirty water. Also since both forms of hypochlorite will tend to increase the pH of the water, it is essential to keep the pH down towards 7.2 in order to maintain chlorine activity (ie hypochlorous acid).

Bathers should not enter the pool until the chlorine level has fallen to 5 ppm and it is best to do that by natural decay by leaving any covers off the pool rather than trying to use sodium thiosulphate and running the risk of removing all the chlorine, or indeed creating a chlorine demand.