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.
- Empty and clean the pool before refilling and treating with chlorine.
- 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.
One 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.
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).
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.
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.
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.
Maintaining the correct pH level in a spa or hot tub is crucial. One of the reasons why it is so vital is to ensure that the sanitiser works to its full potential, which in turn makes sure your water is safe to bathe in. One of the big advantages of using bromine as your sanitiser instead of chlorine is you can maintain a pH level between 7.2 – 8.2 instead of 7.2 – 7.6. The reason for this is that bromine is an active sanitiser at a higher pH level so it will continue to kill any bacteria in the water even when the pH level goes beyond 7.6. On the other hand chlorine loses its killing power when the pH level goes over 7.6. Therefore using bromine allows you more flexibility when controlling the pH level which is particularly beneficial for hard water areas where the incoming water supply naturally contains high pH and alkalinity levels.
If you are refurbishing your pool filter over the next few months are you aware that there is now an alternative filter media to silica sand, which is becoming increasingly more popular amongst pool owners?
Eco Glass Filter Media (EGFM) is the environmentally friendly and cost effective filter media that is made from recycled glass such as old wine bottles and jam jars. Not only is it environmentally friendly but it also offers many other advantages over silica sand.
EGFM is more efficient allowing you to save on backwashing and the resultant water, energy and chemical treatment costs.
- Its angular to sub-angular particle shape and bound silica content provides a 30% improvement in turbidity removal over silica sand.
- It generally removes finer particles from water than the equivalent grade of silica sand.
- Its non porous composition means it is less likely to ‘clump’ or channel than silica sand.
- With superior permeability, back washes take less time, saving water/sewer charges, and energy and chemical treatment costs.
EGFM is cleaner as it is less susceptible to bio-fouling. Unlike silica sand EGFM particles have a smoother surface, so bacteria cannot get trapped in any cracks or flaws, which means less remedial action and again less chemical treatment to destroy pollutants.
EGFM requires less material as it is less dense than sand, requiring 15% less media to fill the equivalent filter.
EGFM doesn’t degrade therefore has a longer life span and may not need changing even when the filters are due for refurbishment.
As you can probably imagine there is a sophisticated production process in place which turns your old wine bottles into a safe and effective filter media. EGFM is manufactured by a mechanically induced high-speed process that transfers energy into the glass feedstock resulting in the destruction of glass whilst rendering it sharp free. It does not grind, mill, hammer or flail the glass. It does not abrade, so EGFM retains a smooth shiny surface. The end result is three grades of EGFM which are illustrated below. If you are interested in purchasing any EGFM please visit our website.
||Grade 1 (0.5mm – 1.0mm (16/30)). This is the equivalent to 16/30 filtration sand.
||Grade 2 (1.0mm – 3.0mm). This acts as support media.
||Grade 3 (3.0mm – 7.0mm (pea gravel)). This also acts as support media.
We recently came across this article on the Daily Mail website from 2012 which features a recreational pool called Nemo 33 in Brussels, Belgium. The reason why it grabbed our attention is because it has a deep end measuring an unbelievable 34.5 metres and it holds a staggering 660,500 gallons of water!! A bit different to the 10,000 gallon pools we deal with on a daily basis!! The reason for the 34.5 metre drop is because the facility is also used a training facility for divers as well as a recreational pool. Therefore diving is allowed in this swimming pool!
It is around this time of the year when pool owners 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.
- Backwash the filter and clean the strainer.
- 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.
- 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.
- To prevent algae from growing add Winterising Algaecide. The recommended dosing rate is 2.5 litres per 10,000 gallons of pool water.
- Turn on the circulation to disperse the solution through the water for a period of 24 hours.
- 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.
- To protect any exposed metal surfaces, drain the water from the pump(s), filter(s), heater and pipework.
- Leave any valves above the water level open. Any below should be closed to protect from frost damage.
- Switch off the electricity supply to the system.
- Cover the pool with a heavy-duty winter pool cover.
- 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.
Shocking your pool is one of the most important procedures in swimming pool maintenance but we often get a lot of customers asking why it’s so important? So in this blog post I will explain.
The main reason why you need to shock treat your pool is to prevent algae growing in the water. Algae are microscopic plant life that grows very quickly and rapidly in sunny and warm conditions and if they are not killed you will soon be faced with a horrible green mess instead of a nice sparklingly clear pool! The truth is nearly all outdoor pool owners in the UK will have encountered this problem in the past. No matter how good your filtration system is or how vigilant you are with your chlorine levels algae spores will still find a way into your pool water. Commonly this is via dirt from rain or bathers.
Maintaining a free chlorine level between 1 and 3 parts per million (ppm) will kill the majority of algae spores that enter the water but over time the remaining algae spores will build up and develop into algae blooms (green mess). This is especially true in sunny and warm conditions as mentioned earlier. This is where shocking your pool becomes imperative. Once a fortnight, or once a week in the summer, you should use Calcium Hypochlorite Granules (Chlorine Shock) to super-chlorinate the pool and increase the chlorine level up towards 10ppm. This rapid increase in chlorine will obliterate any algae spores that are in the water and it will ensure you maintain a sparklingly clear pool. Remember to let your chlorine level drop back into the recommended range before re-entering the pool.
Just a quick note on why you need to use Calcium Hypochlorite Granules (Chlorine Shock). Calcium Hypochlorite 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 chlorine based 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 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.
Another reason why shocking your pool is important is to reduce the combined chlorine level. This is more applicable to public pools that experience a high bather load but it is important for domestic pool owners to be aware of it as well. When you add chlorine to the pool water it produces hypochlorous acid (HOCl), which is commonly referred to as free chlorine. As noted earlier the free chlorine is responsible for killing bacteria, viruses and algae spores in the pool water but even if you maintain a suitable free chlorine level (1-3ppm) it is inevitable that some pollution will still enter the water. This could be in the form of dirt and algae spores from the rain or perspiration, oils and cosmetics from bathers.
When the pollution enters the water a chemical reaction will take place with the free chlorine. This reaction produces combined chlorine which consists of the chloramines called mono-chloramine, dichloramine and nitrogen trichloride. The mono-chloramine is responsible for the distinct chlorine swimming pool smell and the nitrogen trichloride is very irritating to bathers eyes and noses. Although combined chlorine contains a lot of chlorine (hence the smell) it is all locked away therefore it does not kill bacteria, viruses and algae. So in summary you do not want combined chlorine in your pool.
There are ways in which you could minimise the combined chlorine level without using any chemicals. For example you could use a pool cover when the pool isn’t in use and you could insist that bathers showered before using the pool. Sounds straightforward but the first proposal can be expensive and we all know the latter just won’t happen. Therefore it is important to reduce the combined chlorine level by regularly shocking your pool with an oxidising agent such as Calcium Hypochlorite (Chlorine Shock) or Oxy Shock (Potassium Mono-Peroxysulphate). The addition of either of these chemicals will remove all pollution and reduce the combined chlorine level. In normal circumstances once a fortnight should be adequate but if you experience a high bather load, sustained period of hot weather or a substantial rainstorm then you may need to shock your pool once a week.
Finally although I have talked about combined chlorine you don’t need to worry too much about testing for it. Providing you shock your pool regularly a domestic family pool should not encounter any of the problems caused by combined chlorine. However if you are interested in testing for combined chlorine you can revisit a previous blog.