Frequently Asked Questions


Iron and Manganese

Iron (Fe) and manganese (Mn) are responsible for a number of problems with water supplies. Above 0.3 mg/L iron and 0.05 mg/L manganese, these contaminants cause aesthetic problems such as discolouration of water, turbidity, staining and unpleasant taste.

The presence of iron and manganese can also accelerate biological activity further exacerbating taste, odour and colour problems.

Chlorine dioxide selectively oxidises the relatively soluble Fe (II) and Mn (II) to insoluble Fe (III) and Mn (III or IV) species. The resulting precipitate of insoluble iron and manganese compounds are removed by fi ltration or sedimentation followed by filtration. Any remaining Fe (II) and Mn (II) is removed by hydrated iron and manganese species coated on the filter media where the trapped ions are oxidised to the insoluble form.

In addition, chlorine dioxide can oxidise organic complexing agents which assist in keeping iron and manganese in solution. In some cases the chlorine dioxide works by destroying biofilms that encapsulate organically bound metal ions preventing them from being oxidised by conventional oxidising biocides.


Many industrial processes cannot tolerate the presence of iron in the feed water. The problem may be unacceptable colour or taste (in food related industries) or it may be the presence of iron promotes unacceptable growth of bacteria.

Chlorine dioxide rapidly oxidises Fe(II) to Fe(III) which then precipitates as iron hydroxide:

ClO2 + 5Fe(HCO3)2 + 3H2O 5Fe(OH)3 + 10CO2 + H+ + Cl-

Optimum reaction conditions are neutral to slightly alkaline. Above pH 5, approximately 1.2mg/L chlorine dioxide is required to remove 1.0mg/L iron.

The resulting precipitate is reported to be 99% removed by a 45 micron sieve above pH 5.


Above a concentration of 0.05mg/L, manganese causes “black” water, discolouration of laundry, encrustation of water mains, deposits on taps and industrial machinery as well as adversely affecting the taste of drinking water and beverages.

Chlorine has been used to control these problems but the reaction rate is very slow and manganese can still be present at unacceptable levels even after 24 hours contact with chlorine.

Chlorine dioxide rapidly oxidises manganese to manganese dioxide which can then be removed by filtration at the treatment plant. Reaction is complete in less than 5 minutes under favourable conditions.

Optimum reaction conditions are neutral to slightly alkaline:

Above pH 7: Mn2 + ClO2 + 4OH- + MnO2 + 2ClO2- + 2H2O

Below pH 7: 5Mn2+ + 2ClO2 + 6H2O + 5MnO2 + 12H+ + 2Cl-

Above pH 7, it requires approximately 2.45mg/L chlorine dioxide to remove 1.0mg/L manganese.

Dose Rates

Dose rates will depend on the level of contamination of iron and manganese and other species present in the water as well as the degree of control required.

As a general rule, CleanOxide Liquid 75 should be dosed continuously upstream of the filtration system allowing CleanOxide Liquid 75 and complete oxidation of the iron and manganese species. pH control may also be necessary to ensure optimum removal of iron and manganese.

CleanOxide should not be dosed with lime or activated carbon which will inactivate the chlorine dioxide.

If chlorine dioxide is also being used as a disinfectant, further dosing of CleanOxide Liquid 75 after the fi ltration step may be required particularly if an activated carbon filter is used.

The table below can be used as a guide to estimate the minimum amount of CleanOxide 75 required per megalitre (million litres) of water to remove iron and manganese. If both are present, as is often the case, the quantity of CleanOxide required is the sum of the amounts for each individual contaminant.

Approximate volume of CleanOxide Liquid 75 required to remove iron and manganese from water at pH >7

Iron (mg/L)

CleanOxide Liquid 75 (L/ML water)

0.1 16
0.2 32
0.3 48
0.4 64
0.5 80
1.0 160


Manganese (mg/L)

CleanOxide Liquid 75 (L/ML water)

0.01 3.3
0.02 6.5
0.05 16
0.1 33
0.2 65
0.5 160

For further advice on applications of CleanOxide 75, contact us to discuss your specific requirements.

Please Note: The information contained in this document is based on Natural Water Solutions CleanOxide Liquid 75 pure chlorine dioxide and is not applicable to other sources of chlorine dioxide.

Conventional methods of generating chlorine dioxide have in the past limited the use of chlorine dioxide. These limitations included the cost of the equipment, the complexity and hazards of generating and handling chlorine dioxide safely and the accompanying by-products including chlorine, chlorites and chlorates.

The presence of chlorine in chlorine dioxide generated by classical methods was responsible for the perception that chlorine dioxide is a corrosive substance. Chlorine dioxide generated by acidifying sodium chlorite solutions (sometimes called stabilised chlorine dioxide) can also be highly corrosive due to the presence of excess acid.

Pure Chlorine Dioxide is non-corrosive

Pure chlorine dioxide whether present as a gas or as a solution in water is not corrosive. Chlorine dioxide does not hydrolyse in water to form acidic compounds – it remains in solution as chlorine dioxide.

Natural Water Solutions has developed an innovative and highly effcient method of generating a chlorine dioxide solution of very high purity without the need for any complex or costly equipment and without any hazardous or corrosive by-products. We call this solution CleanOxide Liquid 75.

When freshly made, CleanOxide 75 is a 0.75% (7,500 mg/L) solution of pure chlorine dioxide in water. When used at the recommended dose rates, CleanOxide Liquid 75 is not corrosive.

Chlorine Dioxide Corrosion Data

Note that a corrosion rate <1.0mpy is considered non-corrosive.

304 and 316 Stainless Steel

Test Solution

Result after 10 days soak test at 40°C

Vapour Corrosion

4ppm ClO2 initially; 20ppm ClO2 after 12 hours (produced by acidifying 500ppm sodium chlorite solution to pH 2.7) Corrosion of both 304 and 316 stainless steel No Corrosion of either 304 or 316 stainless steel
100ppm pure ClO2 (pH 7.2) 2.5L No Corrosion of either 304 or 316 stainless steel

Reference: Bohner, H.F., Bradley, R.L. Corrosivity of chlorine dioxide used as sanitizer in ultrafitration systems, J. Dairy Science, 1991, 74, 3348

304 Stainless Steel


Corrosion Rate (mpy)

25ppm ClO2 (pH 4) for 4 weeks (see note 1) 0.010
5ppm ClO2 (pH 4) for 4 weeks (see note 2) 0.010
5ppm ClO2 (pH 6) for 4 weeks (see note 2) 0.000


  1. 25ppm pure chlorine dioxide solution buffered at pH4 with phosphate buffer. Solution changed every other day.
  2. 5ppm pure chlorine dioxide solution buffered at pH4 and pH6 with phosphate buffer. Solution changed every other day.

Other Data

  1. Freymark, S.G. and Raub, J.S. Selective oxidation of industrial Wastewater contaminants by chlorine dioxide, Proceedings Mid Atlantic Industrial Waste Conference, University of Delaware, Newark, Delaware, June 19 – 20, 1978This review article describes the use of chlorine dioxide in a number of applications. In one plant cooling water application, replacement of chlorine with chlorine dioxide resulted in a significant reduction in corrosivity towards carbon steel and admiralty steel.
  2. Costilow, R.N., Uebersax, M.A. and Ward, P.J. Use of chlorine dioxide for controlling microorganisms during the handling and storage of fresh cucumbers. J. Food Science 1984, 49, 396The authors reported that the corrosion of equipment by low levels of chlorine dioxide at near neutral pH is much less than when chlorine is used.
  3. Pacheco, A.M., Durham, H.E., Dhilon, R. and Edward, C. The use of chlorine to control microbial growth in an ethylene glycol contaminated cooling tower – a case history, CTI Annual Meeting, 1989, TP89-14In this cooling system, process leaks and the high levels of chlorine required to achieve microbiological control resulted in admiralty corrosion rates of 3mpy and carbon steel corrosion rates of up to 24mpy. Corrosion rates of both admiralty and carbon steel improved using chlorine dioxide. Admiralty rates after chlorine dioxide use were not stated but carbon steel rates were reduced to <2mpy.

Please Note: The information contained in this document is based on Natural Water Solutions CleanOxide 75 pure chlorine dioxide and is not applicable to other sources of chlorine dioxide.

In most large scale water treatment plants, mixing of CleanOxide Part A (P) and CleanOxide Part B takes place in an automated preparation plant such as the one shown schematically below.

CleanOxide Batch Dosing System

CleanOxide Part A (P) and CleanOxide Part B are allowed to react for approximately seven hours before CleanOxide Liquid 75 is ready to dose into the water supply. In practice, sufficient product is mixed every day to treat the required volume of drinking water.

Plant capacity can be increased by installing more than one holding tank for CleanOxide Liquid 75 or the frequency of filling and discharging the holding tank can be increased (up to three times per day is possible).

The preparation plant itself is constructed from HDPE with HDPE or PVC pipes. The preferred material for the wetted parts of pumps is Teflon for maximum durability.

The operation of the preparation plant is under the control of a plc and can be remotely monitored if required. Cross checks on the operation of the preparation plant can be carried out to ensure the quality and integrity of the CleanOxide Liquid 75 produced by monitoring both the volume of raw materials delivered to the mixing vessel and the weight of material delivered.


CleanOxide Liquid 75 Part A and CleanOxide Liquid 75 Part B are available in 18L/2L, 180L/20L and 900L/100L (5 x 20L) pack sizes (sufficient to make 20L, 200L or 1000L CleanOxide 75 respectively).

CleanOxide Part A (P) and CleanOxide Part B for professional users are available in 1000L pack sizes only.

For more information, please get in touch.

The dose rate of CleanOxide Liquid 75 is determined by the quality of the water to be treated and the level of treatment required.

Experience in Europe suggests that treatment rates of 0.1 to 0.3mg/L chlorine dioxide are adequate where water quality is high.

Lower quality water or water containing impurities that consume chlorine dioxide (such as manganese or iron) may require considerably higher doses to achieve satisfactory levels of disinfection. As a general rule, water that requires higher levels of conventional chlorination will also require higher levels of treatment with CleanOxide.

When chlorine is the primary disinfectant, 0.05 to 0.2mg/L chlorine dioxide is usually adequate to control undesirable taste and odour problems.

When treating any system with chlorine dioxide for the first time, it is usually necessary to “shock dose” the system at a rate at least double the maintenance rate required.

The reason for the shock dose is to remove biofilm that has built up in the system and not controlled by conventional chlorination.

The exact amount of the shock dose required and the duration of the shock treatment is site specific and will depend on many factors.

Experience suggests one to two days at a high dose followed by one to two days at a moderate dose is adequate to flush most systems that have been well maintained on a conventional chlorine disinfection routine.

The Table below illustrates the volume of CleanOxide Part A (P) and Part B required per megalitre (ML) of drinking water per day at 0.1 to 1.25mg/L chlorine dioxide.

The volume of CleanOxide 75 produced when these materials are mixed is also included in the Table.

Volume of CleanOxide Part A (P) and CleanOxide Part B required per megalitre (ML) of water per day

Dose Rate(mg/L) Part A (P)(L/day) Part B(L/day) Water mixed with Part A(L/day) CleanOxide 75(L/day)
0.1 0.67 1.33 11.3 13.3
0.2 1.33 2.66 22.71 26.7
0.3 2.00 4.00 34 40
0.5 3.35 6.70 56.95 67
1.0 6.67 13.34 113.99 134
1.25 8.34 16.68 141.98 167

For further advice on treatment rates, please contact us.

Chlorine Dioxide (CIO2) is an oxidising biocide. It kills micro-organisms (bacteria, viruses and spores) by attacking and penetrating their cell wall, disrupting the transport of nutrients across the cell wall and inhibiting protein synthesis.

Since this action occurs regardless of the metabolic state of the organism, oxidising biocides are effective against dormant organisms and spores (Giardia Cysts and Poliovirus).

Chlorine Dioxide is highly soluble in water as well as in a variety of organic material. Because it is so soluble, Chlorine Dioxide penetrates through materials that protect micro-organisms from other biocides.

For example, in water systems, bacteria can be protected by a polysaccharide film (biofilm). Chlorine has difficulty penetrating this barrier because of its ionic nature in water. However, Chlorine Dioxide readily penetrates through this layer to kill underlying organisms.

Although Chlorine Dioxide has the word Chlorine in its name, they have completely different chemical structures. The additional oxygen atom radically changes the molecule and creates completely different chemical behaviours and by-products.

Their differences are as profound as those between hydrogen, the explosive gas, and hydrogen combined with oxygen, which creates di-hydrogen oxide – commonly called water.

CleanOxide™ is 99.9% pure stabilised Chlorine Dioxide and generates no harmful By-products. Furthermore it’s effective over a wide pH band from 4 to 10.

In contrast, Chlorine changes the taste and odour of water. Chlorination will also produce harmful by-products called Trihalomethanes (THMs) and Bromates which are carcinogenic.

Moreover, Chlorine will not remove biofilm, is more corrosive, environmentally unsound, may not be used at temperatures of 40°C or over and has a very narrow pH band within which it has any useful action (6.5 to 7.5).

Food Standards Australia / New Zealand (FSANZ) General Food Standard 1.3.3

Chlorine dioxide is permitted as a processing aid in packaged water and water used as an ingredient in other food.

Australian Pesticides and Veterinary Medicines Authority (APVMA)

Chlorine dioxide is exempt from the requirements for approval of a technical grade active constituent.

Australian Drinking Water Guidelines

The Australian Drinking Water Guidelines (the ADWG) published by the National Health and Medical Research Council (NHMRC) and Natural Resource Management Ministerial Council (NRMMC) in 2004 are not mandatory standards but provide a basis for determining drinking water quality.

Chlorine dioxide has been approved by NHMRC for use in disinfecting drinking water since 2005. The ADWG recommends a maximum of 1mg/L for chlorine dioxide on health grounds and a maximum of 0.4mg/L on aesthetic grounds (taste).

According to the ADWG, drinking water may need to be dosed at 1 to 1.25mg/L chlorine dioxide to achieve a residual concentration of 0.4mg/L.

The main impurities associated with chlorine dioxide are chlorite and chlorate. The ADWG recommends a maximum value of 0.3mg/L chlorite on health grounds but currently does not have any recommendation in relation to chlorate due to insufficient data being available. New guidelines are expected to be published in the near future which will recommend a maximum value for chlorite of 0.8mg/L and 0.3mg /L for chlorate.

These guidelines have been developed by reference to conventional methods of generating chlorine dioxide that are associated with high levels of both chlorite and chlorate.

CleanOxide Liquid 75 is a solution of 7500mg/L chlorine dioxide with a maximum chlorite concentration of 75mg/L. At the maximum dose rate of 1.25mg/L chlorine dioxide suggested by ADWG, chlorite concentration from CleanOxide 75 would be less than 0.0125mg/L, far below the recommended maximum.

National Health and Medical Research Council

Chlorine dioxide is approved for disinfection of drinking water in Australia (National Water Quality Management Strategy, Australian Drinking Water Guidelines 6, 2004, National Health and Medical Research Council)


US EPA has approved chlorine dioxide for the following applications:

  • Bactericide and fungicide for hard non-porous surfaces in hospitals, laboratories and medical facilities
  • Bactericide and fungicide for instruments in hospitals and dental facilities
  • Dental pumice disinfectant
  • Disinfection and deodorisation of ventilation systems and air conditioning duct work
  • Final sanitising rinse for food contact surfaces in food processing plants, restaurants, dairies, bottling plants and breweries
  • Disinfection of environmental surfaces such as walls, floors and ceilings in food processing plants, restaurants, dairies, bottling plants and breweries
  • Disinfection of water systems aboard aircraft, boats, mobile homes, off -shore drilling rigs, etc.
  • General disinfection and deodorisation of animal confinement buildings such as kennels, barns, pig pens and poultry farms
  • Treatment of stored potable water
  • Sanitising rinse for uncut, unpeeled fruit and vegetables


  • P-1 approval for bacterial and mould control on environmental surfaces in federally inspected meat and poultry processing plants
  • D-2 approval as final sanitising rinse not requiring a water flush on all food contact surfaces in food processing plants

More information

For more information, see the Australian Government Department of the Environment website.

No. Chlorine dioxide as a disinfectant has the advantage that it directly reacts with the cell wall of micro-organisms. This reaction is not dependent on reaction time or concentration. In contrast to non-oxidizing disinfectants, chlorine dioxide kills micro-organisms even when they are inactive.

Therefore the chlorine dioxide concentration needed to effectively kill micro-organisms is lower than non-oxidising disinfectant concentrations. Micro-organisms cannot built up any resistance against chlorine dioxide.

Remove the CleanOxide tablet from the bag and add it directly to the water source that needs treatment.

If you are using a large quantity of tablets we recommend you first add the tablets to an empty bucket or container and then distribute evenly into the water source. Alternatively add the tablets to a nylon or hessian bag and suspend in the water body. We recommend dosing in the evening for best result.

It depends on the incoming water source. For clean water such as stored potable water or rainwater, we recommend a maintenance dose every quarter. If you notice discolouration, odour or bad tasting water, then reapply the maintenance dose.

CleanOxide is $20/bag + GST + Freight.

CleanOxide comes in 2 varieties:

  • 20 grm Tablets: Five tablets per bag.
  • 4 grm tablets: Eight Tablets per bag

Chlorine Dioxide test strips are also available for measuring the Chlorine Dioxide residual in your water. Chlorine Dioxide test strips are $40/bottle (50 test strips in a bottle)

There is a bulk discount when buying a box of 25 bags with CleanOxide tablets. Contact us for more information.

For a standard treatment or precautionary dose:

  • 1 X 20g CleanOxide tablet treats up to 2000L water
  • 1 X 4g CleanOxide tablets treats up to 400L water

If you are treating more water than is stipulated, you can use a larger quantity of tablets but we recommend waiting 48 hours until consuming the water. This will enable the excess dosage to break down naturally.

I.e. if you’re treating 3000L use 2 x 20g tablets and wait 48 hours before consuming.

High bacterial levels and odour issues are common for old tanks. We recommend to dose at twice the standard treatment dose in this circumstance.

For example: 1 x 20g tablet to treat 1000L and 1 x 4g tablet to treat 200L. We recommend then leaving the water for 48 hours before it is consumed.

If the standard dose rate is used, then the water will be safe to drink within 12 hours.

If you are using a shock dose (more than the standard does) we recommend waiting a minimum of 48 hours before consuming the water.

Especially following the first treatment, we recommend that you flush the lines as biofilm might have dislodged during and after the treatment.

Besides sanitising the water, CleanOxide assists in removing biofilm on the tank walls and in the pipes which means it may be useful to use CleanOxide even when the water is already of high quality.

Yes. There is Liquid CleanOxide 75 which we recommend to treat larger water tanks. However, due to its potency, this should be applied by professionals. Contact us for more information.

Alternatively you can reduce the tank water level when using tablets for treatment.

Natural Water Solutions do not conduct bacteria water testing but we would recommend you have an independent test conducted if you are really concerned about your water quality. Ideally, you should do a test before and after dosing CleanOxide.

No. CleanOxide is a biocide which will damage the fish’s gills and kill them over time. For fish ponds, we recommend using BiOWiSH.

Yes. CleanOxide treated water is safe to use for gardens.

Wait for 48 hours after dosing if the treated water feeds into your washing machine. Test the first wash on 1 or 2 old coloured clothes to make sure they don’t get bleached. (Chlorine Dioxide is a natural bleach.)

Yes, CleanOxide Chlorine Dioxide removes tannin discolouration from the water.

In case of extreme discolouration, we recommend using double the normal dosage of CleanOxide Chlorine Dioxide and waiting 48 hours before consuming the treated water.

Yes, it’s safe to shower and wash if you have used the standard dose. If you have used a larger dosage we recommend waiting 48 hours.

CleanOxide Gel

No, but we recommend to keep CleanOxide Gel out of reach of children and to also avoid potential spillage.

Yes, subject to the contamination the CleanOxide Gel might last longer.

Yes, stir CleanOxide Gel powder with spoon provided.

No, the CleanOxide Gel is no longer effective once it goes a clear white colour.

If using CleanOxide Gel in a car or hot environments the gel will liquify and spill if knocked over or tips over.

Chlorine Dioxide Test Strips

Efficacy of Chlorine Dioxide

Chlorine dioxide does not react with water or ionize in water, it is present in solution as molecular chlorine dioxide. For this reason, it is able to diffuse into organic matter including micro-organisms and biofilms. It is effective against all micro-organisms including algae, bacteria, bacterial spores, fungi, fungal spores and viruses. In high concentrations it can be used to control some higher organisms.

Chlorine dioxide shows good efficacy at very low dose rates. For example, experience in Europe has shown that drinking water can be maintained to the required standard when treated with <0.3mg/L or PPM of chlorine dioxide. The rate at which chlorine dioxide kills micro-organisms depends on the concentration of chlorine dioxide, temperature, and species of organism. Chlorine dioxide is noted for the speed with which it kills micro-organisms. Some typical values for Log 4 (99.99%) reduction of various bacteria in water at 20°C with a chlorine dioxide concentration of 1.5mg/L or PPM) are listed below:

  • Escherichia coli 2 min
  • Enterococcus spp. 10 min
  • Coliform 2 min
  • Legionella pneumophilia 15 min
  • Fecal coliform 10 min
  • Fecal streptococcus 10 min

Mode of Action

The mode of action of chlorine dioxide is that of an oxidizing agent. It simultaneously attacks many cell components particularly certain amino acids found in protein. This results in rapid denaturing of proteins, including enzymes, in the cell membrane and cell contents resulting in cell death.

The rapid inactivation of many different enzymes simultaneously accounts for the speed with which chlorine dioxide acts.


Because of its non-specific mode of action, micro-organisms cannot develop resistance to chlorine dioxide.