Frequently Asked Questions

These pages have been designed to assist both home pool owners and commercial pool operators with answers to a range of frequently asked questions, as well as understand commonly used terms.

These questions cover a wide range of pool problems including what chemicals to dose to achieve a desired result and how to calculate the dose rate etc.


Now that schools are required to have NZQA qualified water treatment operators to operate school pools from October 2002 onwards, what do I do and where is training available from?

Your local school support should be able to give you the contact details of the person or organisation that is offering these courses in your area. If not, your school should have received information from companies such as Opus or Watermark Consultancy Ltd who specialise in offering these courses.

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How to calculate a swimming pool volume.

Firstly measure the pools length, width and depths in metres. Once you have the dimensions you then need to multiply the length by the width and then multiply this answer by the average of the depth. The answer that you get will be in cubic metres (m3). To change the volume to litres simply multiply this volume by 1000. When calculating a pool volume the volume of the balance tank and pipework etc is normally disregarded. E.g. A pool measures 25 metres long by 15 metres wide and is 0.9 metres deep in the shallow end and 1.5 metres deep in the deep end. The average depth of the pool in this example is 0.9 plus 1.5 divided by 2. This equals 1.2 metres. To calculate the pool volume, multiply 25 by 15 by 1.2, which equals 450m3 or 450,000 litres.

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What does a turbid water or a chloramine smell mean? How do I reduce it?

A chloramine smell indicates that the disinfection process is not working to the desired levels to maintain healthy clean pool water. In simple terms the way to fix it is to add more chlorine or the disinfectant of choice. Usually water with a high chloramine level will also look flat or milky and will be more irritating to swimmer's eyes and skin as well as have a noticeable obnoxious chlorine smell. Firstly test both the FAC and TAC and from these calculate the CAC or chloramine level, also test the pool's pH. NZS 5826,2010 sets the levels for these parameters. Once you have established the chemical levels of the pool water compare it to the standards and increase the disinfectant feed to the pool. If the pH is outside of the normal or prescribed range correct this as well by dosing the appropriate chemical. Also check the filter to ensure that it does not need a backwash, if it does, do it as soon as possible, as the water flow and thus turnover rate of the pool has probably slowed considerably due to the increased filter pressures that are present. If the problem exists in a commercial pool, consideration must also be given to the number of swimmers that have been using the pool as over loading a pool beyond its filters or disinfection systems capability is a very common cause of this problem. NZS 4441, 2008 sets the maximum loadings a commercial pool can have depending on its volume, filter area, turnover and water temperature. It is important not to exceed these loadings. All commercial pools should be well aware of there maximum allowable loadings and have management strategies in place to meet their obligations.

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What does green water usually mean? How do I fix it?

Green water indicates that algae are present in the pool water. If left the algae will very quickly grow to form a thick covering over the pool walls and floor. As some pool based algae are not affected by chlorine this problem may not always be simply remedied by the shock dosing of chlorine. If the algae is chlorine resistant the use of an Algaecide such as Algaetroll will be required. Such algaecides are normally safe for swimming at normal dose rates, check the label before you dose. Once the algae is destroyed by the chlorine or algaecide, it can be removed by a combination of constant filtration and vacuuming of the pool bottom. If the algae has grown on the pool walls it will need to be brushed off with a long handled broom or pool brush prior to vacuuming. It may be necessary to vacuum the pool several times before the pool is clean. If filtering through a sand filter the use of a flocculent such as Alfloc will greatly increase the filters performance and speed up the recovery period.

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How do I dose cyanuric acid and how do I test for it?

Cyanuric Acid comes in a granular form and unfortunately is very hard to dissolve due to its composition. This difficulty in dissolving Cyanuric Acid should not dissuade you from using it as it has a dramatic effect on reducing the chlorine consumption of your pool on a sunny day. The best way to dose it into a pool with skimmer boxes is to dissolve it in hot (not boiling) water and stir thoroughly. Mix no more than 0.5 kg of product with 8 litres of hot water in a 10 litre bucket. Once thoroughly mixed carefully and slowly pour the liquid solution into the skimmer. Be careful not to pour any undissolved chemical into the skimmer as it is very abrasive may damage the pump. Repeat the process until the required dose of chemical has been dissolved and dosed into the skimmer, remember this may take some time so be patient as the result is worth it. For a pool with a balance tank slug dose the product into the far side of the balance tank well away from the pump suction.

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How do I calculate how much Cyanuric Acid is required?

Firstly you need to know your pool volume in cubic metres (m3). You also need to know the amount of Cyanuric Acid you wish to dose per m3. If you were starting with fresh water then a level of between 25 to 50 grams per m3 (g/m3) would be appropriate. If you already have a residual of Cyanuric Acid in your pool water you need to test this level using an appropriate test kit. NZS5826, 2010 indicates both the frequencies of testing and target levels for Cyanuric Acid. Once you have a test result, subtract his result from the target level you have selected, use the following formula. Multiply the pool volume (m3) by the amount of Cyanuric Acid required (g/m3). This will give an answer in grams so divide this by 1000 to convert it to kilograms.

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What should I maintain my chlorine residual at?

NZS5826, 2010 states the acceptable chlorine levels that all pools, from home pools to commercial, that should be maintained at all times to ensure healthy bathing conditions.

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What should I maintain my pH at?

NZS5826, 2010 states a range of 7.2 to 8 with a most desirable value of 7.4 to 7.6.

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What does pH mean and why is it important?

pH is the measure of how alkaline or acidic a water sample is. The range is 0 to 14 with 7 being neutral. From 7 to 0 is increasingly acidic while from 7 to 14 is increasingly alkaline. pH is an important aspect of water chemistry as its level dictates the efficiency of chlorine. In simple terms chlorine is more active in lower pH levels of say 7.7 and lower and less active in the upper levels above 7.7. In general terms this means that more chlorine will be required to achieve the same level of disinfection in water of a higher pH than a water with lower pH. pH also dictates which form or forms of chloramines are present in a water. In general terms water with a lower pH will tend to form trichloramines while water with a higher pH will tend to form mono and dichloramines.

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How often should I backwash my filter?

All filtration systems should come with a well documented operating manual that should include backwash frequencies. If this is not the case a good rule of thumb would be a 2psi rise in pressure differential for a Sand Filter. In the case of Pressure or Vacuum Media Filters you should consult the supplier for site specific instructions so as to avoid damage to the filter or harm to the operator. It should be remembered here that as filter pressures increase the recirculating flow rate will decrease. This means the pool turnover time will increase.

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What does alkalinity mean and why is it important?

Alkalinity is the measure of the capacity of water to neutralise acids or alkalis, primarily because of the presence of bicarbonates, and provide a buffer against dramatic pH changes.

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Do I need to adjust alkalinity in my pool?

Only if it is outside of the recommended levels. NZS5826, 2010 gives the recommended levels but in general terms 100 to 110 will give good protection against pH bounce. pH bounce is one of the leading causes of bather eye irritation.

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How do I dose alkalinity and how do I test for it?

Alkalinity is best raised by dosing Sodium Bicarbonate (baking soda) to the pool. This will have a large effect on alkalinity and a smaller effect on pH. A variety of test kits are available to test alkalinity from inexpensive home pool test kits up to more accurate equipment. Once you have measured your pools alkalinity you need to subtract the result from the target value that you have selected. Once you have decided on the amount required in grams/m3, you then multiply this value by your pool volume in m3. This gives the total amount of Sodium Bicarbonate to be dose in grams so divide this answer by 1000 to convert it to kg. Sodium Bicarbonate can be dissolved in a bucket of warm water and slowly dosed into the skimmers with the pump going or "slug" dosed into a balance tank well away from the pump suction or overflow channel.

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How often do I need to vacuum the pool?

For a public facility it should be every day and for a home pool once a week may suffice depending on external factors such as usage, trees, grass and wind etc. If a pool is not vacuumed frequently enough then it may look good prior to any one getting into it but after a small amount of use it becomes turbid. When this happens the aesthetic appeal of the pool vanishes and users are more prone to getting debris in their eyes. In the worst case scenario, a turbid pool is dangerous as bathers cannot be seen below the surface so there is an increased risk of drowning.

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What is Total Water Balance and how do I determine the water balance of my pool water?

Total Water Balance is the correlation between several chemical parameters that determine whether water is either scale forming or corrosive. There are some different scales to quantify this correlation with the most popular being the Langlier Saturation Index and Ryznars Scale. There are several ways to determine the state of your water in relation to water balance including a section in NZS5826, 2010, slide rule calculators and web sites etc. This is an important aspect of water treatment as it can have a dramatic affect on bather comfort and maintenance requirements. Potable water in New Zealand usually lends itself to producing corrosive water in swimming pools without some form of intervention. At its worst this corrosive nature of the water can lead to very short life spans for expensive items such as heat exchangers and pumps etc. It is recommended that you either research this issue in relation to your pools situation or consult a water treatment specialist such as our company, Ian Coombes Ltd.

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What is the relationship between FAC and TAC?

NZS5826, 2010 states that FAC is to be no less than 85% of TAC. This is to ensure that disinfection is happening to a level that ensures all pathogens etc are oxidised and that the pool water is comfortable and safe for bathers.

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What are Total Dissolved Solids (TDS)?

TDS is the measure of all soluble matter dissolved in water. TDS can only be measured using a meter. These meters are available from Ian Coombes Ltd and vary from small pocket meters costing approximately $250 up to desktop models that start at $800. High TDS levels are best controlled by dilution.

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Do I need to test for TAC?

While it is not a requirement for domestic pools to test for this under NZS5826, 2010, we believe that it is a prudent thing to do. For public pools it is a mandatory requirement to test for TAC and determine CAC residuals.

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Do I need to record pool water test results?

As with above you don't have to in a domestic situation but it would be advisable, as it is useful in trouble shooting water chemistry problems. As above, for public pools it is a mandatory requirement

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How can I tell if I have over chlorinated my pool?

This can be difficult as DPD reagents, which are the most popular test reagents for chlorine, are bleached in chlorine solutions above 5 grams per m3. This leads to inaccurate results above this level. An over chlorinated pool will usually have a strong chlorine smell and look crystal clear and sparkly. This is in contrast to a pool with a high chloramine level that will possibly look turbid or flat. The pool will also not offer good bather comfort and other test results may appear strange compared to normal. To check the chlorine level in this situation you can either do a diluted FAC test or take your water sample to someone offering free testing. To do a diluted FAC test you will need a dilution tube that has various dilutions marked on it. You need to use non-chlorinated distilled water to get an accurate result. To do a 2:1 dilution with a dilution tube you would fill the dilution tube to the 2x mark with pool water and fill the rest of the way with distilled water. Agitate the sample then use it to carry out a FAC test in the normal way. Once you have this result, multiply the answer by 2 to get the actual reading. Depending on how over chlorinated the pool is you may have to go as high as a 50:1 dilution (ie. One part pool water to 50 parts distilled water). If in doubt contact someone who is specialist in water testing for assistance, such as our company, Ian Coombes Ltd. If the pool is over chlorinated do not rely on any other test results for other parameters until the chlorine level has been reduced and a new set of tests done.

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How do I reduce the chlorine level in my pool?

Once the actual FAC level has been established, Sodium Thiosulphate can be added to the pool water at a dose of 500 grams per kg of chlorine that needs to be removed. It is best to dose ½ the Sodium Thiosulphate initially and retest to ensure that the desired effect is being achieved. Once you are sure that the full dose is correct then dose the remaining chemical.

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How do I winterise my pool?

Pools are best left full over winter and the pool water kept in good condition. In broad terms you need to keep the pool bottom clean by either using a debris cover or if you do not have one scooping and vacuuming the pool on a regular basis. If too much organic matter is left to build up algae is too hard to control. To keep algae controlled you need to dose an algaecide such as Algaetrol. You should also keep an effective residual of Cyanuric Acid in the pool. Once a month a maintenance dose of both algaecide and chlorine can be added and the pools filtration system run overnight. In this way the pool water should look great at the start of summer and there will be very little in the way of start up time required. Keeping the pool full also protects it from structural damage from a high water table and keeping the water free from algae also protects pool finishes from staining etc.

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How can I easily increase the filtration performance of my sand filter?

The use of a flocculent such as Alfloc 8013 will improve the filtration efficiency of any sand filter. In simple terms Alfloc forms a gel like coating over the sand bed allowing the sand bed to trap particles that could otherwise pass straight through the filter and back into the pool. Alfloc can be used all the time to help out an undersized filtration system and is also excellent in assisting clearing up a turbid pool. In fact one or two doses of Alfloc is generally all that is required to clear up a very turbid pool that could otherwise take up to a week to clear by itself, if at all. Alfloc is simply mixed with warm water and slowly dosed into a skimmer or balance tank with the circulating pump running.

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How often do I need to test my pool water?

NZS5826, 2010 states the frequency of testing for all chemical parameters for public facilities. If you are a public facility and you do not have a copy of this it would be advisable to get one ASAP. In the mean time contact your chemical supplier for advice. From the standards, domestic pools, pH should be tested twice weekly, FAC prior to daily use, Alkalinity and Calcium Hardness monthly, Cyanuric Acid and Salt levels monthly and Total Dissolved Solids annually.

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What is 'turnover rate' and why is it important?

"Turnover rate" is the number of hours that it takes the entire contents of the pool to pass through the filter once. Relevant New Zealand Standards state the applicable turnover periods for public pools based on pool loadings while there is no set turnover for a domestic pool. The turnover period is important as it is one of the key components to being able to maintain acceptable water quality.

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What is 'Filtration Rate' and why is it important?

The "filtration rate" is a measure of the volume of water that passes through every m² of filter area per second. As above, in the public pool situation there are prescribed rates to meet the relevant standards. If too much water is passed through the filter then the filter will become inefficient and particles will pass through it that would otherwise be trapped. This condition would lead to turbid water that would be very hard to clear.

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What options do I have available to heat my home pool?

In broad terms there is a choice between heat pumps, solar heating along with gas and diesel heating. The later two are generally not that popular, while the first two would make up the bulk of both public and domestic installations. Solar is a good option as long as you have a suitable space of at least 80 to 90% of the pool surface area for a solar collector. Solar also offers a variable temperature as it relies on a warm day to offer heating, periods of inclement weather are a problem. Now that there are very reliable and economical to run heat pumps on the market heating your home pool has never been a better option. The operation of a heat pump is described in the preceding Glossary of Terms.

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What will an Insulating Pool Blanket do for my pool?

An insulating pool blanket constructed from a three layer laminate of woven polyethylene and foam, such as our MacBall or ICL Heat and Energy Saver if used correctly can offer an average increase in temperature of approximately 5°C compared to a pool without a pool blanket. These blankets because of their superior construction offer a life span that is unrivalled by our competitors, 7 to 14 years depending on handling. An insulating pool blanket, as opposed to a bubble cover is imperative if you are using or may use any form of a supplementary heating source such as solar or a heat pump in the future. Blankets will maximise pool usage and extend the swimming season. Also other savings in water, chemicals and cleaning are possible. Our pool blankets come with a three year full repair or replacement on materials warranty. Covers can also be useful in keeping wind blown debris out of the pool when the pool is not in use.

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