Pool and spa FAQs

  1. Why is filtration important to the quality of swimming pool water ?
  2. How do I know when it's time to backwash my pool filter?
  3. When should I ‘vacuum to waste' ?
  4. How should I deal with cloudy pool water ?
  5. Why is pH so important ?
  6. What happens when the pool is too alkaline ? (ie. the pH is high)
  7. What happens when the pool is too acidic ? (ie. the pH is low)
  8. Why is Total Alkalinity (TA) important ?
  9. Why is Calcium Hardness important ?
  10. Why is Total Dissolved Solids important ?
  11. Why do I need to ‘shock' my pool ?
  12. I have an outdoor pool and I am told that I should use a stabilised form or chlorine. Why is that ?
  13. Should I use a flocculant or water clarifier in my pool?
  14. I added algaecide to my pool, but the algae didn't go away. What did I do wrong ?
  15. What causes the tide mark ring around my pool water line ?
  16. Following chemical treatment, how long do I have to wait before I use my pool again ?
  17. How often should I change my spa/hot tub water ?


Why is filtration important to the quality of swimming pool water?

Your filter removes visible matter from the water. The filter medium is designed to remove organic matter, insects, hair, dirt, skin flakes, metal or calcium precipitates and other visible debris that would otherwise cause the water to be hazy and cloudy.


How do I know when it's time to backwash my pool filter?

Your filter medium (usually sand in the case of swimming pools) is designed to trap and remove debris from your pool water. Over time, that debris will obviously build up, gradually reducing the efficiency of your filter. Regular backwashing (ie. reversing the flow of water through your filter) will remove most of the trapped material from your filter medium. Your filter housing should have a pressure gauge which will indicate an increase in filter pressure over a period of time. When this pressure exceeds an acceptable level, it's time to backwash.

Don't forget to clear pump baskets and strainers before backwashing, and remember to run the filter to rinse after the backwash treatment, otherwise much of the debris washed out of your filter medium will simply settle on your filter medium again !

Spas generally use washable/replaceable cartridges in their filter systems; your spa manual should tell you how often to change this cartridge, and how to clean it.


When should I ‘vacuum to waste'?

When you ‘vacuum to waste' you are pumping the debris you vacuum out of the pool and sending the dirty water to waste rather than through the pool filter. If you have a large amount of debris in your pool (silt, or leaves or other organic material), this is a good way to avoid clogging your pump pre-filter and your filter medium. Of course, this process removes a large amount of water from the pool in a short time so make sure the pool is full before you begin, and top up if necessary !  This technique only works with circulation systems which use a multi-port filter valve.

Be sure to monitor the waste outlet where it connects to the sewage system, just in case the sewer line cannot handle the large amount of water pumped through.


How should I deal with cloudy pool water?

Cloudy water is a common problem, with several possible causes, so it is important to approach the problem logically.

First, check to make sure that the pH is within the proper range. Your sanitiser can only function fully within a narrow pH range (7.2 - 7.8 for chlorine, 7.2 - 8.0 for bromine), so this is critical to the smooth operation of your pool.

If the pH is within range, it could be that your ‘free' sanitiser level is low; check your free and total chlorine levels; if the total chlorine exceeds your free chlorine by more than 0.5 ppm, this means that you have high levels of combined chlorine. Combined chlorine is simply chlorine which has become chemically bound to contaminants in your pool. The chlorine is still there, but it is locked away and cannot function as a sanitiser.

High combined chlorine is dealt with by ‘shock' treating your pool using either Shock Chlorine Granules or Oxy Shock.

Try to keep your free chlorine levels between 2 ppm and 4 ppm at all times.

If you have to make large corrections to pH and/or chlorine levels, it will take some time for the pool water to clear afterwards; keep your filter pump running, and consider using a solid flocculant or liquid clarifier (Spa Sparkle) to help your filter do its job.

It is also possible that your filter is simply dirty, and needs to be cleaned. If you have a sand filter, just follow the backwash instructions for your installation, rinsing at the end of the backwash.

Finally, it is possible that you have an excess of fine suspended particles which are too small to be easily filtered out. A flocculant or clarifier will cause these particles to clump together, making it easier for your filter to remove them from your water; a flocculant may cause the particles to sink, in which case you can remove them with your pool vacuum cleaner.


Why is pH so important?

pH is one of the most important factors in pool water balance and it should be tested and adjusted at least three times a week in swimming pools, and every day in the case of a spa or hot tub.

pH is a measure of how acid or alkaline the pool water is. The pH scale runs from 0 to 14; a pH of 7.0 is neutral - below 7.0 is acidic, above 7.0 is alkaline.

The pH of our eyes and skin is around 7.4, and this happens also to be the ideal pH for your pool - try to keep pool pH between 7.2 - 7.8 at all times.


What happens when the pool is too acidic? (ie. the pH is low)

If your swimming pool is constructed from cement, the water will begin to attack the pool walls, creating a surface which is ideal for algae growth. This can also happen with the grouting in tiled pools.

Metal components may corrode - this includes swimming pool equipment, pipe fittings, pump connections, etc.

As the metal pool components corrode, sulphates are formed. These materials can cause staining of pool finishes.

The efficacy of your sanitiser is lost. As a result, your water is not being sanitised effectively.

Low pH can irritate the skin, eyes and nose; swimwear can fade and perish.  


What happens when the pool is too alkaline? (ie. the pH is high)

In alkaline conditions there is a risk that the calcium in the pool water will combine with carbonates to form calcification or scale, just like in an old kettle. This is seen most at the waterline, where the scale deposit can trap dust and dirt, turning black with time.

The swimming pool water starts to become cloudy or murky and it loses its sparkle.

The calcium carbonate has a tendency to ‘plate out' on the sand in the pool filter, effectively turning it into cement. The filter loses its ability to trap dirt from the pool water.

As the pH rises, the power of the chlorine to act on contaminants is lost. At a pH of 8.0, your chlorine has only 20% of the effect you would expect.

Low pH can irritate the skin, eyes and nose.


Why is Total Alkalinity (TA) important?

The total alkalinity (TA) is a measure of the quantity of alkaline substances present in the water. TA is measured in parts per million (ppm), and a figure between 100 ppm and 200 ppm is about right.

When the total alkalinity (TA) is within this range, it prevents rapid pH changes (pH ‘bounce') and helps to stabilise the pH level.

If the TA is too low, this can cause damage to cement walls and grout, corrosion of metal components and staining; in addition, the pool may suffer from pH bounce (random changes in pH rapidly).

If the TA is too high, the pH may become difficult to adjust, the water may become cloudy, and the pool may require constant pH adjustment; in addition, your sanitiser may lose its effectiveness.

It is recommended that you test the TA regularly, but in practice it changes very little in a well-maintained pool.

To raise the level of TA, use Total Alkalinity Increaser (sodium bicarbonate), a little at a time; this will adjust TA without increasing the pH. Use our Chemical calculator to calculate the dose. Raising the TA can be quite a slow process, as the pool water will respond slowly to this agent.

Reducing the TA is also a slow process. Add pH Reducer to the deepest part of the pool with the pump switched off. Again, dose a little at a time, waiting at least 24 hours between applications. Again, use our Chemical calculator to calculate the dose. It could take several days to reduce the TA if it is very high.


Why is Calcium Hardness important?

Water Hardness in general refers to the total mineral content of the water (calcium, magnesium, iron, manganese and other elements). These elements are present in the water used to fill the pool, and the levels can increase through the use of regular pool chemicals (eg. calcium from Shock Chlorine).

However, with pools and spas we are really interested in the calcium hardness levels only.

The ideal range for calcium hardness is 150 - 200 ppm.

If the calcium hardness is too low, the water can become corrosive and may damage the pool surfaces. Metal components may also be damaged.

Low calcium hardness can easily be increased using Hardness Increaser (calcium chloride). The dose can again be calculated using the Chemical Calculator.

If the calcium hardness is too high, you may see scale formation on pool and fitment surfaces, and the pool water may become cloudy.

The only reliable way of reducing calcium hardness is to replace some or all of the water in the pool.


Why is Total Dissolved Solids important ?

Total Dissolved Solids (TDS) is simply a measure of the total amount of dissolved material in the water.

The TDS in the pool is influenced by many factors; the chemicals we add to adjust the pH, chlorine, water hardness, alkalinity, dust, dirt and debris.

The maximum acceptable level of TDS for pools is 1,500 ppm. Above this level there is risk of staining of pool surfaces, and high TDS will also reduce the activity of any treatment chemicals you add; the pool water may become cloudy.

The only practical solution is to drain some or all of the water from the pool and to replace it with fresh water (with a low TDS). You should seek the advice of a pool engineer before draining an in-ground swimming pool. A regular backwashing routine will help to prevent high TDS.


Why do I need to ‘shock' my pool ?

As you use your pool, it is inevitable that debris and contaminants will build up over time, reducing the efficiency of your disinfectant or sanitiser as it is used up. Material such as hair spray, suntan oil, cosmetics, skin cells, urine, perspiration and other organic substances combine chemically with the chlorine in the water to form ‘combined chlorine' (a family of chlorine-containing products called Chloramines).

Once ‘combined chlorine' forms, it can cause eye and skin irritation, and it smells unpleasantly of chlorine. Chloramines contain a lot of chlorine, but it is locked away, and therefore acts as a very poor disinfectant. Because of the smell, pools with this problem are often inaccurately accused of having too much chlorine !

When the combined chlorine level reaches 0.5 ppm or more, it is time to shock your water. Routine shock treatment is necessary to destroy the combined chlorine compounds and restore the chlorine sanitiser to full ‘free chlorine' efficiency. A pool can be shock treated by adding large doses of non-stabilised Shock Chlorine, (this is sometimes referred to as super-chlorination), or by adding a non-chlorine shock agent such as Oxy Shock.

Both treatments accomplish the goal of destroying and removing bather waste and preventing the formation of combined chlorine.

Super-chlorination has some drawbacks. First, Shock Chlorine can be difficult to dissolve, (and you must never add the dry material directly to your pool, or you may damage liners and fittings), and it can upset the pH of your pool water.  Shock chlorination also requires swimmers to wait until the level of chlorine drops below 5 ppm, which can take a day or more, before they can safely use the pool again.

Although more expensive than Shock Chlorine, Oxy Shock allows swimming or bathing almost immediately after application, does not harm pool liners, has easily determined dosage rates and does not upset water balance. Oxy Shock and other non-chlorine shock treatments contain no chlorine, therefore you must make regular additions of sanitiser to ensure that you are still disinfecting the water.


I have an outdoor pool and I am told that I should use a stabilised form or chlorine. Why is that ?

Chlorine is broken down by ultra-violet light from the sun. If stabiliser (also called conditioner), is not present, the chlorine will disappear very rapidly over the course of the day.

With outdoor pools we recommend that you use a stabilised form of chlorine to reduce the rate at which your chlorine breaks down. The stabiliser (usually cyanuric acid) should be kept at levels between 30 - 50 ppm to properly stabilise the pool. The use of a stabiliser will reduce your overall chlorine consumption and save you money.

Our Stabilised Chlorine Granules and Mini & Maxi Tablets are all fully stabilised. Our Shock Chlorine Granules and Liquid Chlorine 15/16% are not, and should be used with indoor pools or for rapid addition of chlorine to outdoor pools.

It is better to use non-stabilised forms of chlorine in indoor pools, because the chlorine is not exposed to sunlight. When using stabilised forms of chlorine, stabiliser levels will tend to build up over time, but regular backwashing (which helps with water turnover) and occasional checks of stabiliser levels will help you keep this under control.


Should I use a flocculant or water clarifier in my pool?

Yes, but not to excess !

Flocculants and clarifiers are designed as an aid to the efficient operation of the filter by coagulating the fine suspended material which causes cloudy and hazy water into larger particles which can be removed by the filter. The presence of this suspended material also increases the sanitiser demand, so regular use of flocculant or clarifier can reduce pool maintenance costs.


I added algaecide to my pool, but the algae didn't go away. What did I do wrong ?

First, it is important to remember that chlorine is an effective algaecide in its own right, so it's always wise to check and adjust your pH and free/total chlorine levels before adding algaecide, and to shock your pool if you have high combined chlorine (chloramine) levels.

Once you have done this, add the correct amount of algaecide according to the directions on the container. If you under-dose, the algaecide may not work properly, and if you over-dose, this can cause foaming in your pool, so accurate dosing with this agent is very important.

In addition to properly dosing your water, we also recommend that you add the algaecide in the morning on a bright sunny day for best results. Algae are plants and therefore grow in the presence of sunlight. If you dose algaecide during the peak growth time this will increase the uptake of the algaecide by the algae and make it more effective.


What causes the tide mark ring around my pool water line ?

The accumulation of oils and dirt from bathers is the biggest cause. It is important to using a pool liner cleaner which has been specifically designed for pools to clean it off - don't be tempted to use household cleaners. Abrasive cleaners can actually dull the tiles or liner at the water tile, many products cause unsightly foaming in your pool, and some can even react with your sanitiser. Our Tile & Liner Cleaner is ideal for use in pools and hot tubs.


Following chemical treatment, how long do I have to wait before I use my pool again ?

With the exception of super-chlorinating (which requires you to wait until the chlorine level drops back to the recommended maximum level of 5 ppm), you can generally use your pool when the chemical is dispersed throughout the water. Fifteen minutes in a spa and one hour in a large swimming pool is a good rule of thumb.


How often should I change my spa/hot tub water ?

You will have to drain and refill your spa or hot tub regularly.

As a rule of thumb, take the volume of your spa in litres, divide by the estimated number of users of the spa each day, then divide by 12. That will give you a guide for the time (in days) between refills.

eg.  2,000 litres, divided by 4 users = 500

500 divided by 12 = 42 days

So, you should drain and refill every 6 weeks.