Testing your pool water!
It's important to regularly test your pool water especially when it is in use, not just to ensure the comfort and safety of swimmers but also to protect your pool from damage which can be expensive to repair. The five most important parameters to measure in your pool are pH, Chlorine, Alkalinity, Salt and Cyanuric acid.
pH
pH is a measure of the acidity of your pool water. It is important to ensure your pools' pH is in the correct range. If the pH is too low, corrosion of pool components and bather discomfort can occur. If the pH is too high, the ability of chlorine to properly disinfect your pool is compromised.
Chlorine
Chlorine is used to kill bacteria and bugs that can live in your pool water.
If the chlorine level is too low bugs and bacteria can breed in your pool making it unsafe for swimming. If chlorine is too high it will be uncomfortable for swimmers (burning eyes etc).
Alkalinity
When the total alkalinity (TA) is within the optimal range, it prevents rapid pH changes and "stabilises" the pH level.
If the TA is too low, you will have difficulty keeping the pH level stable (pH bounce).
If the TA is too high, the pH will be difficult to adjust.
Cyanuric Acid
Ultra Violet (UV) light from the sun interferes with chlorines' effectiveness. Cyanuric acid is used to protect chlorine from the damage casued by UV. Ensuring correct cyanuric acid levels will mean you can use less chlorine.
Salt
For a saltwater chlorinated pool, it is important to have the correct level of salt in accordance with the reccomendations of you chlorinator's user manual. If the salt levels are too low or too high it can damage your saltwater chlorinator.
Equipment
There is a range of equipment availiable to test the safety of your pool water. Test strips and comparators are often used to test home pools because they're cheap and straightforward to use, but are less accurate and reliable than photometers used by professional pool technicians.
Test Strips & Comparators
Test strips & comparators are cheap and straightforward to use but can have problems with accuracy. Both of their accuracy relies on the users judgement and can be more of an art than a science. The accuracy of test strips can also be effected by moisture getting into the bottle and improper handling by the user or if they're used after their expiry date.
Comparator kits often use a liquid chemical to test your pool water. Their accuracy relies on adding exactly the right amount of the chemicals to your sample, one drop too many or too few will give inaccurate results. The liquid chemicals also have a short expiry and have to be regularly replaced.
Photometers
Photometers are simpler, faster and more accurate than test strips or comparator kits. Professional pool technicians can spend thousands of dollars for a top of the range photometer. Digital photometers remove the user error that makes test strips and comparators inaccurate. The results of a photometer are displayed on a digital display that takes the guesswork out of testing your pool water.
Professional results at home
Optimal Levels for a balanced pool
| CHEMICAL | Optimal Value | If you results are low... | If your results are high... |
| Chlorine | 2.0ppm | Shock the pool | Turn chlorinator down |
| pH | 7.4 Summer | Add soda ash | *Add muriatic acid (diluted) |
| Total Alkalinity | 80-120 ppm | Add baking soda (Sodium Bicarbonate) |
**Add muriatic acid |
| Cyanuric acid | 20-50 ppm | Add Cyanuric Acid | Drain pool and refill |
| Salt | 3000-5000 ppm (Chlorinator dependent) | Add salt | Drain pool and refill |
* Add acid by spreading around pool or pour into pool in front of return jet. Pool should be running when doing this so the acid spreads throughout the pool as rapidly as possible.
** Pour acid into a three to five foot circle in the deepest part of the pool while the pump is off. Allow to set for at least 20 minutes before turning pump on.