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Treating Chlorine Poisoning in a Turtle : Estimating Residual Chlorine in a water sample - Immediate Advice Required!

I am a post-graduate student in Veterinary Surgery from Orissa Veterinary College. I am facing a great problem in treatment of an tortoise poisoned with the excess amount of residual chlorine in a well.

Kindly help me in treat the tortoise by providing me information:

1.      What are the adverse effects of residual chlorine on the fresh water organisms particularly on tortoise?

2.      What are the easily available methods and / equipments for estimation of residual chlorine in water body? I have searched on internet and found orthotolidine method. Will it be suitable and cost effective?

3.      Would you please provide me name of some organization or institute in Bhubaneswar from where I can get help regarding this matter?

4.      What is the standard for residual chlorine in drinking water? Is it 0.2mg/lit or 0.5mg/lit?

5.      What is the actual composition of bleaching powder? Is it only hydrated lime or sodium hypochlorite or combination of anything else?

With regards,

Subharaj Samantara
M.V.Sc., Veterinary Surgery,
Orissa Veterinary College,
O.U.A.T., Bhubaneswar-751003, Orissa,
Mob – 09438184509




Dear Subharaj,

The pointwise answer to your query is

1.  The excess amount of residual chlorine in treated water is obviously harmful and poisonous for aquatic life. I exactly does not know that how much dose is harmful fo tortoise.

2. O-tolidine method has been banned in some countries due to its carciogenic effects but this is the best and cost effective method for measuring residual chlorine.

3. You can contact your P.H.E.Department/Fisheries department.

4. The standard for residual chlorine in drinking water is 0.2PPM at tail end of the water supply system.

5. The bleaching poeder is Chlorinated Lime and its formula is CaOCl2 i.e. Calcium Oxychlorite.


Amit Kr. Singh,
Govt. of Haryana,
Public Health Engg. Department,
Water Testing Lab,Karnal-132001(haryana)

2. Chlorine test kits& treatment for chlorine poisoning in a turtle

Dear Mr.Samantara,

How to treat a turtle which has what you call chlorine poisoning is in the domain of veterinarians and not people who are resources persons on water like us on indiawaterportal.

There are chlorine test kits for testing residual free chorine using a colorimetric method.With the proliferation of swimming pools in the country,chlorine test kits should be easily available.You will probable find information on such test kits on this portal itself.For human use,residual free chlorine should be within 0.3ppm in water used for drinking.

Bleaching powder is usually calcium hypochlorite in powder form.Sodium hypochlorite is also available as a liquid.


3. Treating Chlorine Poisoning in a Turtle : Estimating Residual Ch

Dear Ms Subharaj ,

 In my view if Free Chlorine is 0.1 mg/l should not affect the aquatic animals. Atleast I have tried this with gold fishes in my domestic aquarium. O-Tolidine is the suitable method to roughly know the presence of free chlorine.In Bhubaneswar You can test water samples at Palasuni Water testing Lab, PHED . The free chlorine should be 0.2 mg/l in the last tap end of the distribution network, so you can expect more concentration in the pumping stations.The composition of BP is Calcium hypochlorite  with formula Ca(ClO)2.

Detail can be viewed,

sibasis Panda

4. residual chlorine estimation

    *  Bleaching Powder is known as Chlorinated Lime/Chloride of lime etc. Its chemical Composition is CaO 2CaOCl2 H2O. It is used for disinfection of water.
    * Unless the well is chlorinated, residual chlorine should not be present.
    * residual chlorine is the indicator of absence of micro organisms (pathogens) in water.
    * Allowable limits of residual Chlorine in drinking water for human consumotion ranges from 0.2 to 0.5 ppm (mg/l). However, excess residual chlorine is injurious to health. In presence of organic compound if Chlorine is added in excess amount, there is risk of formation of THM which is carcenogenic.
    * Residual Chlorine can be measured with Orthotolidine, OTA methods. It is not at all expensive. However, there are portable Field Test Kits. I am attaching photograph of one such which we are using. Image - Field Test kit
    * You can consult any engineering college in Bhibaneswar (CIVIL engineering/Environmental Engineering Branch) or Institute of Minerals & Materials Technology, Bhubaneswar-751013 for detection of residual chlorine etc

5. Treating Chlorine Poisoning

Dear Subharaj,

Please find below the answers to your questions.

   1. Tortoises (land turtles) are not really that sensitive to chlorinated water as fish or amphibians, although such water can be irritating particularly to the eyes. The limit of residual chlorine in water set for humans applies equally well to tortoises also. Chlorinated water may however destroy the beneficial bacteria affecting the nitrogen cycle and the breakdown of waste products.


   2. I find the procedure given by the WHO at as best suited to determine the residual chlorine in water.


   3. Not known.


   4. According to the 2006 international reference points for standard setting and drinking water safety of the World Health Organization (WHO), the limit of chlorine (residual chlorine) in drinking water should not exceed 5 mg/L.


   5. Bleaching powder is calcium hypochlorite with the chemical formula Ca(ClO)2.


I find some ambiguity in your query. Soon after your diagnosis that the tortoise brought to you was poisoned with excess amount of residual chlorine in a well, you must have treated it to regain its health and ask the owner of the tortoise not to chlorinate the well in which it has to live.  

Tortoises are known to have much higher life span than humans. It was a traditional practice particularly in India to keep tortoises in drinking water wells to eat away the organisms harmful to humans and make water safe for drinking.  

The modern method of keeping water in wells safe for drinking is through (shock) chlorination. There is no point in using both the traditional and modern methods for keeping groundwater clean.

Best wishes,

Dr. R. Jagadiswara Rao
Professor of Geology Retired
Sri Venkateswara University
Tirupati, AP 517502

6. Dear Subharaj,   There are

Dear Subharaj,


There are conflicting opinions on whether tap water should be dechlorinated for turtles. Turtles may not be as sensitive to chlorine as fish or amphibians, but it can still be irritating to them (especially their eyes). It is also important to consider that chlorinated water may destroy the beneficial bacteria in the tank, affecting the nitrogen cycle and breakdown of waste products.


O-tolidine method is extensively used for residual chlorine estimation. If you are not very particular about quantitative estimation (which requires a colorimeter), you can use field testing kits. They are commercially available. You can get the contact addresses from India Water portal website.


I am sure you should be able to get help from Department of drinking water and/or state pollution control board regarding chlorine estimation methods.


As per IS 10500:1991, standard (desirable) for residual chlorine is 0.2 mg/L. However it is mentioned that when protection against viral infection is required, it is 0.5 mg/l.


Bleaching powder is usually a mixture of calcium chloride hypochlorite, CaCl (OCl); calcium hypochlorite, Ca (OCl) 2; and calcium chloride, CaCl 2.



Best wishes


Leela Iyengar




7. Dear Subharaj,

Dear Subharaj,


Chlorination of water supplies and polluted waters serves primarily to destroy microorganisms.

  1. Chlorination adversely effects aquatic life.
  2. Orthotolidine method is best method.
  3. Standard for residual chlorine is 0.2mg/L.When protection against viral infection is required it should be min. 0.5mg/L.
  4. Composition of bleachingpowder is mixture of calcium hypochlorite ca(ocl)2 and cacl2+ca(oH)2.H2O .

 With regards,


M.V. ShashiRekha

Chief Chemist

Department of Mines and Geology


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