Measuring Chlorine in a Swimming Pool or Hot Tub

Loading... 67 view(s)
Measuring Chlorine in a Swimming Pool or Hot Tub

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.

DPD Tablets

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:

DescriptionCode Measures Suitable for
Domestic PoolTesters & Hot Tubs Kits    
Pool & Hot Tub Test Kit158010Cl 0.5-6mg/l
Br 1.1-13.2mg/l
pH 6.8-8.2
hot tubs
Traditional Cl/pH PoolTester (Orange Box)151601Cl 0.5-6mg/l
pH 6.8-8.2
hot tubs
5in1 Multi PoolTester151900Cl 0.1-3mg/l
Cya 20-200mg/l
TA 20-800mg/l
CaH 20-800mg/l
hot tubs
Tablet Refill Pack 5in1 PoolTester515980  1515900
Electronic PoolTester Scuba II216100-17Cl 0-6mg/l
Br 0-13.5mg/l
pH 6.8-8.4
Cya 1-160mg/l
TA 0-300mg/l
hot tubs
Professional Instruments    
MD100 3in1 Photometer278011Cl/pH/Cya pools
hot tubs
MD100 3in1 Photometer278060Cl/pH/Alk pools
hot tubs
MD100 3in1 Photometer278110Cl/pH/Br Hot Tubs
using chlorine or bromine
MD100 6in1 Photometer278091Cl/pH/Br/Cya/TA/CaH  
MD110 6in1 Photometer2980902Cl/pH/Br/Cya/TA/CaH With Bluetooth
DPD No1 Rapids pk100511310BT  PoolTesters
DPD No1 Rapids pk250511311BT  PoolTesters
DPD No3 Rapids pk100511290BT  PoolTesters
DPD No3 Rapids pk250511291BT  PoolTesters
DPD No1 pk100511050BT  Photometers
Scuba II
DPD No1 pk250511051BT  Photometers
Scuba II
DPD No3 pk100511080BT  Photometers
Scuba II
DPD No3 pk250511081BT  Photometers
Scuba II
Pool and hot tubs choline testing systems from Lovibond.
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:

Camlab can supply a comprehensive range of test kits for swimming pool and hot tub testing. Please contact us for further information.

This blog article was supplied by the technical department at Lovibond.

Leave your comment
Your email address will not be published