The Langelier Index

The Langelier Scale, later to become the Langelier Saturation Index (LSI) , was originally developed by Dr Wilfred Langelier. It is a very accurate way of determining water balance and is often used by builders and poolshops.

The LSI is mathematical calculation that takes into account four factors: pH, Alkalinity, Calcium Hardness and Temperature. A minus figure is under-saturated and corrosive while a positive figure is over-saturated and has a tendency for scaling to occur. The accepted limits are -0.5 to 0.5 . Perfectly balanced water has an LSI of 0.

The LSI can be interpreted as the pH change required to balance the water.

A positive LSI means you should lower your pH (add acid).
A negative LSI means you should increase your pH (add soda ash or buffer, depending on alkalinity).
NOTE: Buffer primarily increases alkalinity and as a side effect increases pH, while Soda Ash will only increase your pH.

We only adjust these variables because you cannot adjust temperature and calcium hardness easily.

To make it easy for you to calculate the LSI for your pool we have provided a FREE program that will do it for you. By adjusting the various levels you can test and then correct your balance. Try adjusting your figures and see what works best.

See our software

Sydney Water Restrictions

For those living in the Sydney, Illawarra and Blue Mountains areas, mandatory water restriction have been in place since October 2003. The latest information on water restrictions is available from Sydney Water [link below].

Level 3 restrictions (June 1, 2005) do not affect the topping up of pools but do affect the filling of new or renovated pools.  You must apply for a permit to fill a new or renovated pool over 10,000 litres. You must apply for a permit to fill a new or renovated pool. A renovated pool is one which has had substantial changes to it’s shape or major additions to the structure. To obtain a permit you will need to install indoor water efficient appliances, which are available from Sydney Water.

You ARE allowed to leave a hose unattended filling a pool or spa.  You may also hose hard surfaced areas briefly if any chemical has been spilt, if brooms or other waterless alternatives cannot clean up the spill.

You ARE allowed to fill a pool or spa, as long as waterwise procedures are adopted.  The amount of evaporation in your pool does not change with the depth of the water.  As a result we recommend customers allow their pools to fill with rainwater or to fill them with a hose to a higher level.  This means it will be a lot longer before you have to add water to your pool again and it also means there is less chance of damage to your equipment from lack of water.

Fix any leaks in your pool or spa.  If you are losing more than 1″ of water a week you may have a leak.  Check the backwash line (to the drain) and the equipment for leaks when the system is operating.

Spas must be emptied every 4 months for health requirements.  There is no way to avoid this without the water becoming unhealthy.  Use the water to water your lawns and gardens.  Properly sanitised pool or spa water is healthier than tap water.

Backwash only when necessary and if possible run the water onto a lawn or garden.  Properly sanitised pool or spa water is healthier than tap water.

Cartridge or D/E filter elements should be cleaned on a grass area witha hose that has an on/off trigger nozzle or similiar and, if possible, with a device that limits the flow of water to 10 litres or less per minute [required for exempt businesses].

Cartridge filters use less water than a sand or diatomaceous earth filter.  To hose a cartridge using a pressure cleaner or jet nozzle should only require up to 15 litres of water.  Backwashing a filter can use up to 350 litres per minute.

Solar Covers can help reduce the amount of evaporation from a pool however they may not suit all pools. A suction cleaner will not operate properly underneath a solar cover and solar covers will still allow leaves to sink into the pool. See Information section for more on solar covers.

See: Sydney Water


Chlorine is used in a wide range of applications, not just swimming pools. It is a good pesticide or sanitiser. It is produced commercially from electrolysis of salt water (sodium chloride) similar to a salt chlorinator or the ocean, which produces more than man ever has every day.

Chlorine comes in a number of forms including liquid, gas or solid. Calcium Hypochlorite is the standard granular chlorine used in swimming pools. Liquid chlorine or Sodium Hypochlorite is actually weaker with 1 litre being equivalent to 1 cup of granular chlorine. Liquid however is faster acting as it is already dissolved in solution. Pools that use liquid chlorine a lot will find a rise in their Total Dissolved Solids (TDS) level which is due to the salt content.

The other common forms of chlorine are as a stabilised granule or tablet, most commonly Dichloroisocyanurate (Dichlor) or Trichloroisocyanurate (Trichlor). Dichlor has 2 chlorine atoms to every molecule while Trichlor has 3 making them a more highly concentrated chlorine. These two chlorine compounds contain stabiliser (isocyanuric acid) and when dosed in the pool the chlorine and stabiliser must separate in reaction. If there is too much stabiliser or too much chlorine then the reaction that splits these chemicals does not properly occur. This is what is more commonly known as ‘chlorine lock’ and does not allow enough active chlorine into the water. Adding unstabilised chlorine will allow the reaction to occur and allow the tied up chlorine to be broken up and become active. This is why you should not solely rely on stabilised chlorine as a pool sanitiser. Adding stabiliser separately and using normal chlorine will not only be just as effective but it is also significantly cheaper. It is recommended on the packaging of these products not to use them if the stabiliser level is over 50mg/L. Above this you should use an unstabilised chlorine.

Chlorine residue, from granular chlorine, is the result of mixing the chlorine with lower grade materials. Pool chlorine is usually 65% chlorine. The compounds that make up the extra volume are what have the greatest effect on price. Cheaper chlorine will be mixed with lower grade compounds resulting in anywhere up to 30% of the granules not dissolving, while better quality chlorine can be up to 99% – 99.9% soluble.

Weak chlorine is also known as bleach. Be careful handling chlorine, as it will destroy clothing.

Chlorine can be neutralised. Sodium Thiosulphate will reduce chlorine levels dramatically and the no.4 test solution is actually 10% sodium thiosulphate. We would not normally add this to swimming pools unless absolutely necessary. Too high chlorine is not usually a problem and chlorine will dissipate with sunlight. As a warning in fibreglass or vinyl pools suddenly reducing the chlorine level can exacerbate staining.

What about the alternatives? There are a number of alternatives for chlorine advertised on the market however not all of them are as effective a disinfectant. The Australian Pesticides and Veterinary Medicine Association (APVMA) regulates approved pesticides or sanitisers. Their list of approved pesticides currently only includes chlorine, bromine and hydrogen peroxide. This means that chlorine should be used with most of these alternatives anyway to ensure the water is sanitised properly. Bromine is actually a better sanitiser than chlorine and is primarily used in spas, where chlorine evaporates due to the higher temperatures. Bromine however can also irritate skin and can have an overpowering odour. It also accumulates and can build up a high residual level in spas over the years. Bromine is also very acidic and affects pH greatly. This can lead to heater corrosion and the pH should be monitored regularly. A high Bromine level can also cause test kits to show false pH readings, so always use a few drops of neutraliser solution. Spas should be drained every four months for health reasons, although brominated spas should be emptied every few weeks. As spas are significantly smaller than a pool they can be effectively sanitised using chlorine or bromine alternatives.

Only 15 major elements makes up 99.5% of the human body and chlorine is the 10th. A different 15 major elements make up 99.5% of the earth’s crust, including air and water, and chlorine is the 11th. It is one of the most common elements in nature and is even more plentiful than carbon. The oceans release approximately 3 million tonnes of methyl chloride into the atmosphere each year, while in addition 5,000 – 15,000 million tonnes of inorganic chlorine is thrown into the atmosphere as sea mist (between 3-35% of this remains in the atmosphere, while the rest will return to the sea). [Chlorine Online]

85% of medicines, including many life saving drugs, are made using chlorine chemistry. 98% of western Europe’s drinking water is sanitised with chlorine. 25% of medical devices contain chlorine, including blood bags, tubing, heart catheters, prosthetics and x-rays. Chlorine is required to produce protective safety equipment, communications equipment and microprocessors, including telephones, radios and computers, sporting equipment, including soccer balls, surfboards, and skis, house construction, including window frames, plumbing, paint, glue and concrete, and in many consumer products and cosmetics. [Chlorine Online]

Greenpeace stated in 1994 that ‘Of more than a hundred chlorine containing organic materials, the carcinogenic effect has been proven’. This is true but this is because there are no carcinogenic materials only carcinogenic doses as everything is a carcinogen, depending on the dosage ingested. Large studies overseas have shown that chlorine and it’s use in the manufacture of PVC and other products is actually less dangerous than most alternatives, even natural ones. A study conducted in the Netherlands actually looked at chlorine and it’s associated risks and found it to be an incredibly safe and healthy product, which is why it is used worldwide. [The Chlorophiles]

As you can see, chlorine is a very safe and abundant chemical which while toxic in it’s purest form, it is safe in the forms we commonly use it today. By chlorinating your pool or spa you are killing all bacteria and putting oxygen into the water. This is what makes is perfectly safe to drink, shower and swim in.

See: The ChlorophilesAPVMAChlorine Online

TDS (Total Dissolved Solids)

We have had problems recently concerning the maximum allowable level of TDS in public swimming pools. The problem is that TDS includes table salt (NACL). High doses of salt, or liquid chlorine (which contains salt), will increase your TDS possibly above recommended levels even though salt is perfectly harmless. TDS also measures Calcium Carbonate (CACO3) and other salts in the water. If you use powdered chlorine in your pool, or use large amounts of buffer you can increase the level of calcium salts in the water.

The ocean and our ocean pools have a salt content of about 32 ppt, or a TDS of approximately 34000. Yet, even these pools are effectively treated and tested without any problems. So is there a maximum TDS? Can we test easily for TDS? What are we actually testing with TDS? Even we were surprised at what we found and we have included links to the most comprehensive sources.

TDS is a measure of conductivity in water. As conductivity is greatly affected by the amount of salt in the water it can be used as a means of measuring salt content. Conductivity is also affected by temperature.

In Australia TDS/conductivity meters are primarily used to measure the salt level for salt chlorinators. When testing a sample for salt, you must adjust it for temperature difference. Conductivity is compared to known constant values at 25 degrees. This means you must increase your result by 2% for every degree below this and decrease your result for every 2% above this. As most poolshops are testing water at about 20 degrees they should be increasing their results by 12%, although some meters do this calibration for you.

This is trivial compared with the much larger problem of TDS. Conductivity meters can only be calibrated to measure one type of salt at a time, for which the conductivity is known. This means there is no generic TDS measurement, which the swimming pool standards required. Any TDS measurement will be affected by the combination of salts in a pool. This means that for every pool the meter can only be accurately calibrated for that pool and not for any other pool and the only correct way to get a true TDS reading would be to determine the composition of salts in the water (i.e. the percentage of CACO3, NACL and other salts). Without this the TDS readings will not give any useful information. A meter calibrated for NACL for salt chlorinated pools really is sufficient for testing. TDS really is an inaccurate method of testing that has been used for years without much understanding of how it works. It is however the easiest way to test for salt content and is a good guide for those with salt chlorinators. Do not however be concerned about high or low TDS or certain levels of TDS as you can see it is affected by many factors and in salt water pools it will be very high.

See: Practical Considerations for Conductivity and TDS MeasurementReefKeeping – TDS,
PPOA – What is the fuss over TDS?

Oakton TDS Tech Tips [PDF]

Test Kit Instructions

Missing the instructions on your test kit. Here is a refresher.

Solution 1 (yellow)- No longer available now DPD1 Tablet
Solution 2 (red)
Solution 3 (clear lid)
Solution 4 (blue lid)
Solution 5 (green lid)

Chlorine Test
Fill small 10mL container and drop in one tablet (DPD1).
Solution will go purple to indicate chlorine.

pH Test
Fill the other vial to the high mark.
If there is a high chlorine level add a couple of drops of neutraliser (solution 5). If normal, add 1 drop.
For 10mL containers add 2 drops of phenol red (solution 2), 25mL containers use 5 drops.
Solution will change from yellow to purple to indicate pH.

Acid Demand
Complete pH test as indicated above.
Add, by the drop, solution 3 until the solution changes to the ideal color.
In a 50,000 pool for each 2 drops it requires to bring the pH down to the correct level add 500mL of acid.

Alkalinity Test
The large pH containers often have a lower mark for alkalinity, otherwise use a 10mL container.
Add 2-3 drops of solution 4.
Add, by the drop, solution 3 until the solution changes from blue to clear or yellow.
Multiply the number of drops of solution 3 used by 10 and this is your total alkalinity level.

Water Balancing Software
To determine whether your software is correctly balanced use our free water testing software which uses the Langelier index to ensure your water is scientifically balanced. See our software.