Trans Instruments (S) Pte Ltd

5 Jalan Kilang Barat #06-04/05 Petro Centre 159349 Singapore ,

The swimming pool is an excellent environment for the transmission of contagious diseases. Hence, it is very important to maintain proper water quality.

Regular water testing is essential as it monitors the water quality of the pool. Any deviation in water quality parameters will be detected immediately, as you will able to refer to previous readings.

Water Balance

Water balance is defined as a condition whereby the water is neither corrosive nor scale forming. These water parameters: pH, total alkalinity, calcium hardness, temperature and total dissolved solids (TDS) affect the water balance.

To avoid corrosive conditions which can etch pool surfaces and mechanical parts, it is essential to maintain all water quality factors within their proper ranges. Proper levels allow the water to become saturated and non-corrosive which is a key goal for pools and spa operation. When water becomes oversaturated with dissolved substances, especially calcium salts also known as calcium carbonates, these substances fall out of the solution and settle on pool surfaces. This is called scale formation and is a menace to pool surfaces especially plumbing fixtures, since it will clog water lines and filters.

Since water balance is so important in maintaining the pool surfaces and parts, it needs to be constantly monitored with test equipment.


pH refers to the concentration of hydrogen ions in water. pH identifies a substance as acidic, neutral or basic. A substance with a pH of 7.0 is neutral. A substance with a pH below 7.0 is acidic. A substance with a pH above 7.0 is basic.

The ideal pH for pool water is slightly basic, between 7.2 and 7.6. This range is most comfortable for the swimmer. It also protects the pool equipment and allows the sanitizer to disinfect properly.

Why test pH?
pH is considered the best indicator of overall "pool health". The control of pH is critical for protecting the pool and its equipment from costly damages due to corrosive/acidic water or scale-forming/basic water.

When pH is too low When pH is too high
Corrosion of pool equipment/staining Scale accumulates on pool equipment  
Swimmer eye irritation Swimmer eye irritation
Etching plaster pool surfaces Cloudy, turbid water
Chlorine dissipates quickly Chlorine sanitizing power is weakened

Since pH is one of the most vital tests performed daily on pool water, Trans Insruments has developed the Senz pH tester. This instrument is a handy, pocket size tester, which is very accurate and simple to use. Just dip the sensor in the water and read the display after it has stabilized. Easily calibrated by just dipping in standard solutions, this simple maintenance will keep the unit always accurate. The product offers a one-year measurement regardless of the number of tests you perform in a day.


Chlorine is widely used in the disinfection of swimming pools.
Chlorine combines with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl).

Cl2+ H2O HOCl + HCl

Effective Chlorination in Swimming pool:

It is the hypochlorous acid produced in the reaction that provides the disinfecting and potent oxidising characteristic of the chlorine solution.

The amount of hydrochlorous acid produced in chlorinated water is highly dependent upon the pH value of the solution.


The HOCI is in equilibrium with the hydrogen ion and the hypochlorite ion. Any changes in pH of the solution will cause the equilibrium to change. As depicted by the curve below, HOCl decreases and OCl- increases as pH increases. At low pH, almost all the free chlorine is of the molecular form HOCI and at a pH of around 7.5, the ratio between HOCI and OCI- is 50:50.

Hypochlorite ion (OCl-) is a slow acting sanitizer while the molecular form of HOCl is a fast acting sanitizer. Since HOCl acts 80 to 100 times faster than OCl- , it is of more importance than its counterpart OCl-.

How do we measure the effectiveness of pool disinfection?

There has always been a misconception that measuring the amount of chlorine is equated to the effectiveness of pool disinfection. The most effective way to measure disinfection is by measuring the reactions that chlorine in the pool produces. Many studies have shown that the killing rate of the bacteria E.coli in swimming pool water is dependent on Oxidation Reduction Potential (ORP or Redox) and not the free residual chlorine levels.

Oxidation Reduction Potential (ORP)

Oxidation Reduction Potential (ORP) or Redox is a measure of the oxiding properties of the sanitizer in water;  the activity strength of HOCI.  With a value of 600mV, the kill time of E.Coli bacteria is 30 seconds. Above 700mV, the bacteria is killed within a few seconds.

To ensure good water quality, it is necessary to maintain a Redox level of 650mV to 750mV.  Trans Instruments offers the Senz Redox. This instrument is a handy, pocket size tester, which is very simple to use. Just dip the sensor in the water and read the display after it has stabilized.

ORP value also depends on the pH of the pool water. Normal pH values for pool water is 7.4 to 7.6 pH with a tendency to increase to around 8.0 to 9.0 pH depending on the level of contamination. The pH of the pool water has to be maintained with appropriate chemical dosing. Redox readings are affected by fluctuations in pH, therefore it is important to check pH level first before using the Senz Redox tester. The pH must be between 7.4 to 7.6 to obtain an accurate reading.

Total Dissolved Solids (TDS)

Total Dissolved Solids (TDS) refers to the amount of dissolved substances or minerals within the pool which are actually charged ions. These substances enter the pool either through the original water supply or through the addition of treatment chemicals. As the water evaporates, TDS remain behind and over time, the levels become higher and higher.

High TDS readings may produce cloudy water and could cause corrosion. TDS levels should be kept under 2000 parts per million (ppm). If the TDS levels exceed this amount, part of the pool should be drained and replaced with fresh (low TDS) water.

Since, it is the dissolved minerals in water which conduct electricity, a TDS probe or instrument can be effectively used to measure TDS in parts per million (ppm). Trans Instrument's Senz TDS and Senz TDS-2, are self-contained digital pocket size conductivity meters with cell and automatic temperature compensation. They provide quick and accurate reading. All you need to do is to turn the testers on and dip into the sample solution. Any irregularities of the conductivity can be corrected by adding water.