Guidelinesforusing a pooltester/residual chlorinecomparator
After chlorinating a water source or container one of the simplest ways to test if the right chlorine dose is givenis to measure the Free Residual Chlorine (FRC). The presence of FRC in water proves that enough chlorine has been added to treat the water or in other terms to react on all matter present in the water, including micro organisms, and leaving someextra chlorine (residual) in the water to deal with possible recontamination (such asduring handling etc.) The measurement of Free Residual Chlorine is most easily done using a comparator also commonly called a «Pool tester» and tablets (called DPD1) that will be added to the water in the comparator, and that will react and change the colour of the water if residual chlorine is present.
How to use a pooltester/comparator.
- Rinse the Pool tester 3 times with the water to be tested, including the cover. If a syringe is used to fill the pooltester, it should be rinsed inside and outside thoroughly with the water to be tested.
- Fill the 3 compartments to the top with the water to be tested.
- Put one DPD 1 tablet in the right hand or pink coloured compartment(measurement of Free Residual Chlorine) Prevent touching the tablet with dirty hands!
- Replace the cover tightly (it is normal that some liquid is pressed out) with the arrows pointing towards the coloured reference scale.
- Shake until the tablets are completely dissolved (about 20 seconds).
- Read the results in natural day light, comparing the colours in the outside compartments (sample) with those in the central compartment (reference). The residual chlorine level is the level at which the sample colour is similar to the central compartment. A darker pink indicates a higher residual chlorine level no colour change indicates the water is not chlorinated or not sufficiently chlorinated to have a residual chlorine level
- After testing empty pooltester and rinse again
IMPORTANT
- Chlorine takes time to kill all the organisms so the chlorine should be in contact with the water for at least 30 minutes
- For step 1 and 2 always make sure that you the quality of the water you’d like to test does not change: let water flow for a few moments before taking it from a tap. Be careful when pouring water out of a container: let it flow before taking your sample. If using jerrycans, fitted with a tap, do not use the tap to fill the pool tester, as the taps being placed next to the ground are often soiled (leading to false results).
- Never touch the tablets with, the inside of the pool tester or the inside part of the cover with dirty your fingers: this could affect the results. Never use tablets that have fallen on the ground.
- DPD3 can not be used to determine free residual chlorine.
- Only whole DPD1 tablet must be used. Do not use broken tablets (while opening packaging or because of bad storage).
- Tablets have a shelf life of 5 years.The expiry date is written on the outside of the 500 tablets cardboard boxes.
Required residual chlorine level
Condition of water / Contact time / Recommended Free Residual Chlorine / Acceptable chlorine levelpH< 8 / 30 minutes / 0.5 mg/l / 0.2-1.5 mg/l
pH > 8 / 60 minutes / 1.0 mg/l / 0.5-1.5mg/l
Important
- In most waters the required free residual chlorine should be 0.5mg/l. In water with a pH of more than 8 chlorine is less efficient and a residual chlorine level of 1.0 mg/l is recommended.
- If chlorine level in the water is source is below 0.2mg/l it is recommended to increase the chlorine doses at the water source.
- If chlorine levels are too high one has to reduce the chlorine doses at the water source when treating again the same water source. Water with a high chlorine dose (eg 2mg/l) is still safe for consumption but the taste will be affected.
- Residual chlorine levels in water will reduce over time retreatment might be needed when water is stored over longer periods (eg in a bladder)
- To find the right chlorine doses to treat water one has to do bucket testing (see separate guidance sheet)