Chlorine is the most popular disinfectant used in swimming pools throughout the UK. The level of chlorine is dependent on your requirements and procedures laid down in your Pool Technical Operating Procedure (PTOP).
Once set, the chlorine level should be tested regularly and again, this should be specified in the PTOP but as a guideline, a minimum of three times a day would be recommended. For domestic users, the water should also be tested regularly and always before the initial use of the day. There are normally two chlorine measurements made, the free (available chlorine) and the total amount of chlorine. From this, the combined chlorine (used up) can be calculated: total chlorine – free chlorine = combined chlorine.
Combined chlorine is not wanted as it causes the ‘chlorine’ smell and irritation experienced by some users. Ideally, the level of combined chlorine should be zero and certainly no more than 1mg/l. As a guideline, a ratio of free to combined chlorine should be no more than 2:1. I.e. if the free is 2mg/l then the total should be no more than 3mg/l so a combined of 1mg/l or less.
Chlorine is usually measured using DPD tablets. DPD (DPD: N, N-Diethyl-p-Phenylenediamine) is a harmless indicator that goes pink-red in the presence of chlorine. Please note, the range is limited and above 6mg/l the colour developed is taken out by the chlorine and fading or in some cases, complete loss of colour is seen (this is known as bleaching). There are a number of different DPD tablets available, each for testing a specific type of chlorine.
What does each DPD tablet test?
- DPD No1 = Measures free chlorine
- DPD No1 + DPD No2 = Measures monochloramine and free chlorine
- DPD No1 + DPD No3 = Measures combined chlorine (total & free chlorine) by difference adding DPD 3 to DPD 1
- DPD No4 = Measures total chlorine
Chlorine Testing Options from Lovibond
For more information on pool and hot tub chlorine testing from Lovibond please view the following:
|Domestic PoolTesters & Hot Tubs Kits|
|Pool & Hot Tub Test Kit||158010||Cl 0.5-6mg/l|
|Traditional Cl/pH PoolTester (Orange Box)||151601||Cl 0.5-6mg/l |
|5in1 Multi PoolTester||151900||Cl 0.1-3mg/l|
|Tablet Refill Pack 5in1 PoolTester||515980||1515900|
|Electronic PoolTester Scuba II||216100-17||Cl 0-6mg/l |
|MD100 3in1 Photometer||278011||Cl/pH/Cya||pools|
|MD100 3in1 Photometer||278060||Cl/pH/Alk||pools|
|MD100 3in1 Photometer||278110||Cl/pH/Br||Hot Tubs|
using chlorine or bromine
|MD100 6in1 Photometer||278091||Cl/pH/Br/Cya/TA/CaH|
|MD110 6in1 Photometer||2980902||Cl/pH/Br/Cya/TA/CaH||With Bluetooth|
|DPD No1 Rapids pk100||511310BT||PoolTesters|
|DPD No1 Rapids pk250||511311BT||PoolTesters|
|DPD No3 Rapids pk100||511290BT||PoolTesters|
|DPD No3 Rapids pk250||511291BT||PoolTesters|
|DPD No1 pk100||511050BT||Photometers |
|DPD No1 pk250||511051BT||Photometers |
|DPD No3 pk100||511080BT||Photometers|
|DPD No3 pk250||511081BT||Photometers|
Abbreviations used: Br = Bromine, CaH = Calcium Hardness, Cl = Chlorine Cya = Cyanuric Acid, TA = Total Alkalinity
For further information on regulations and legislation please use the following links:
- HSE website:
- The Swimming Pool and Allied Trades Association (SPATA) has a page dedicated to Coronavirus related updates.
- Pool Water Treatment Advisory Group website:
This blog article was supplied by the technical department at Lovibond.