Not bothering with water balance tests? You're asking for trouble!

Posted by on Thursday, May 19, 2016 Under: Pool Water Chemistry
swimming pool water balance testing

Balanced water testing is something that swimming pools should be doing weekly in order to determine whether pool water is 'balanced'. This refers to whether the water is corrosive or scale-forming, or neither (balanced).

Corrosive water is contains little calcium (soft water) and is therefore ‘hungry’ for that substance. It will eat away at anything that contains the calcium it needs. Tile grout is usually high in calcium and is therefore very vulnerable to attack from corrosive water. 

Scale-forming water does the opposite of corrosive water and instead of eating away at things it will deposit a scale on them (you're likely to have seen the effect of this on the heating element of your kettle if you live in a hard water area). It does this because it contains high amounts of calcium (hard water) and will readily give up this excess calcium onto the various surfaces it comes into contact with. This scale-forming can be a problem if it is allowed to build up on the inside of pool circulation pipework etc. where it will affect pipe diameters and flow rates. It also looks unsightly, especially on darker surfaces.

The aim of good water balance management is to have water that is neither corrosive, nor scale-forming (i.e., balanced). The main factor that drives the need for good water balance is planned preventative maintenance (PPM). This is different to the tests for chlorine and pH levels, where the main factor is bather safety and reducing the risk of cross-contamination. Therefore, the water balance test results are lower priority than the chlorine and pH test results. This does not mean that the water balance tests should be neglected though because if they are, the result could be many thousands of pounds worth of remedial maintenance repairs and replacement parts further down the line.

Step 1. 
Carry out tests and note results for:
  • Calcium hardness
  • Total alkalinity
  • Pool water temperature  
  • Total dissolved solids

Step 2.
Convert the results from the above tests to factors as indicated in the tables below (figures in bold provide a worked example).

Step 3. 
Add the factors for temperature, calcium, alkalinity to the pH (there is no factor for pH).

Step 4. 
Minus the factor for TDS from the figure obtained in step 3.

The ideal result is somewhere between 0.1 - 0.4. The pH level is the value that has the most impact on water balance test results. A high pH would contribute to scale-forming water, a low pH would contribute to corrosive water. However, it is not advisable to start adjusting pH levels just to try and get good water balance results, as pH is a critical factor in the efficiency of your disinfection and coagulation, both of which are more important than water balance results. Better ways to either increase or decrease the water balance result are listed below:

To increase: 
Increase the levels of calcium hardness by adding calcium chloride 
Increase the levels of total alkalinity, by adding sodium bicarbonate 
Reduce the TDS levels (if they are particularly high) by diluting with fresh water.

To decrease: 
Take a look at your pH result. If it's high, you need to decrease it anyway as your chlorine is not going to be as effective at higher pH levels
Reduce the levels of calcium hardness by diluting with fresh water
Reduce the levels of total alkalinity by diluting with fresh water.

In : Pool Water Chemistry 

Tags: "swimming pool water balance tests" 

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