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Get The Balance Right Robbie Phillips and Richard Lamburn, STA’s Technical Pool Plant Team, look at water balance – get it wrong and it can cause serious damage not only financially, but to a company’s reputation too!


ater balance is a concept that can aid the management of pool water quality. It is based on a calculation derived from the measurements of pH, alkalinity, calcium hardness, temperature and TDS (Total Dissolved Solids). A relatively simple formula has been developed by the industry over a number of years where the water can be deemed: • Balanced – no tendency to lay down scale or be aggressively corrosive. • Corrosive – will be aggressive and corrode and/or erode metals, concrete, screed, grout etc. • Scale forming – will tend to lay down scale and outside recommended parameters can block pipes, cause rough edges and affect other plant parts. So if we study these particular facets of water balance, we can begin to realise the adverse effects that the whole or parts of the water treatment system can have on a pool facility if not managed correctly – they can be radically costly to repair and can cause potential injury situations.

METHODS Indexes are calculations that determine how far away the current conditions are from an ideal pool water quality condition. There are two methods commonly used: Langelier and Palin tests. Whichever method is used there will be a numerical indication of the water balance condition for any facility – pools, spas etc. When the Index is negative, the water is corrosive. When the Index is positive, the water is scale forming. The Palintest Water Balance Index is a simplified version of the Langelier Saturation Index and has been created with the aim of making it applicable and easy for use in pools. Water Balance equations and rules are useful for understanding the different interactions in your pool, but are not to be used for control alone.

Cut foot due to lost tile grout

The figures should be treated as ideal ranges and not as precise target values.

43_SPN_June_16_STA.indd 43

Advanced corrosion at deck level overflow

PARAMETERS TESTED • Total dissolved solids (TDS) are the sum of the weight of soluble material in water. This can build up due to various reasons. Mains water, for example, can sometimes have a TDS of several hundred mg/l. Disinfectants and other pool chemicals will inevitably produce significant TDS levels, of chloride and sulphates in particular. TDS should not be allowed to rise more than 1,000 mg/l above source mains water, with an absolute maximum of 3,000 mg/l. • pH – how acidic / alkali the water is. • Total alkalinity – measure of the alkaline content of water. • Calcium hardness – measure of calcium salts in water.

TEMPERATURE If the Langelier index is positive, the water is scale forming. A zero result indicates the water is in perfect balance, such that lime scale is just on the point of forming. The ideal operating range is + 0.1 to + 0.4. This indicates that the water is very slightly scale forming. This is desirable, because this will lead to a slight coating of lime scale being formed which will help protect pipe work from corrosion and erosion.

So if we study these particular facets of water balance, we can begin to realise the adverse effects that the whole or parts of the water treatment system can have on a pool facility if not managed correctly…”

Advanced corrosion in header tank

SO HOW CAN THIS BE COSTLY IN TERMS OF FINANCIAL AND CUSTOMER SATISFACTION? In a recent real case, we saw a pool that had neglected to take and analyse water balance test results over a number of years causing continual corrosion (as pictured here). This resulted in tile grouting being corroded and tiles being broken exposing sharp tile edges. The position became intolerable and it was decided to close the pool; the following impact was experienced: • Closure for eight weeks • Loss of income and custom • Capital works costs of over £100,000

ESSENTIAL TRAINING It is essential that all operators are versed in calculating and adjusting the water balance. STA PPO Level 3 certificate covers this aspect in detail. Can you or your operators afford not to be qualified? STA 01922 645097

SPN June 2016 43 24/05/2016 21:32

SPN (Swimming Pool News) June 2016  

Informing the pool and spa industry since 1959. Covering the UK's wet leisure market, SPN (Swimming Pool News) is the UK's longest running a...

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