Posted on 29th Apr 2011 @ 10:42 AM

Everyone talks about water balance, but what is it all about and what are we trying to actually do? There are many different things (parameters) that we can test for your average swimming pool. the most common are pH, Chlorine levels, Alkalinity, Hardness, Cyanuric acid, (stabilizer) and if required the Salt level. There are also many minor parameters that can be tested such as various metals, iron and copper being the main two, as well as magnesium levels etc. On your average pool, these rarely, if ever, require testing.

Essentially we are trying to achieve two outcomes when we test and balance water. On the short term, safe swimmer comfort, in the longer term the protection and care of your pool.

Swimmer Comfort

The two big ones here are Chlorine and pH. Chlorine is added to most pools as a sanitiser. This is to kill any potential bacteria and algae in the pool. If your pool is being correctly maintained, the water will be a sterile environment. The second parameter is the pH level. pH is a scale from 1 to 14 with 7 considered neutral. Below this is an acid, above it is alkaline. In most pools the correct range can be anywhere between 7.2 and 7.6 depending on the finish of the pool. Generally a pH below 7.4 may cause eye irritation leading to the classic “big red buggy-eye” look most pool owners blame on high Chlorine levels.

Protect that Pool!

pH a parameter that is also tested to protect the surface and equipment in the pool, when related to other parameter levels in the pool sample. When tested on it’s own it, it will only provide an idea of swimmer comfort. For this reason it is always worth using your local pool shop for a complete test and balance on a regular basis, rather then relying on basic supermarket style test kits all the time.

When your local pool shop is testing your pool sample, it will compare your results to a series of ranges that your water parameters should fall between. There are no “exact” magic numbers. The goal of balancing your water is to achieve a chemical point where your pool is protected from long term harm. Pool shops work with a set of tables called the Langelier index. These are a set of tables that allow your service technician to lay down an invisible layer of calcium scale over everything in contact with the water. When water is “out of balance” it will try and achieve two things, one is to get rid of excess calcium as unsightly deposits, the other is to try and absorb calcium. In the case of fibre glass and concrete pools this can readily be found in the walls of your pool. The Langelier index was first developed in the 1800’s to protect municipal water pipes in cities, it has since been adapted for use in swimming pools.

Water Balance

Perfect balanced water is the point where we achieve a Langelier index of 0.0. In order to do this, your service technician will compare the Alkalinity to the Calcium or hardness level, then, taking into account the approximate water temperature, will use the Langelier index tables to calculate what is known as the “pH of Saturation”. This is the point where your pool is achieving it’s maximum level of protection. The final goal then is to make the actual pH of your pool meet the Saturation point. To calculate the final Langelier index, your pool shop will then subtract the pH Saturation point from the actual pH to produce a final number. Ideally 0.0, however a range of +/- 0.3 is considered normal.

It should be noted that different pool surfaces require different levels of protection. These are taken into account along with manufacturers guidelines to provide the ultimate protection for your pool. Vinyl pools are a chemically inert surface that does not require water to balanced to in accordance with the Langelier index, instead normal manufacturer guidelines are used.

Author:
Wes Field
Service Manager