Latest Updates



Click for seminar details


KOI logo (135)
Who are we?




Effective dechlorination     (Ensuring effective dechlorination)


Ensuring proper dechlorination of show vats and spare water reservoirs at Koi Shows and in the home pond

Chlorine in water supplies and its effect on Koi
Chlorine is added to drinking water supplies to make it safe for human consumption and, in tap water supplies, it can take different forms. The two most commonly known forms are free chlorine and chloramine.  In fact there are three different types of chloramine and there will probably be another by-product called trihalomethane. All these are toxic to fish.

Haemoglobin in the red blood cells in fish blood picks up oxygen atoms at the gills and transports them around the body giving oxygen to cells that need it before returning to the gills to pick up more oxygen. This process repeats continuously.

If any form of chlorine is in the water, as the haemoglobin passes through the gills, it is affected in such a way that it becomes incapable of carrying oxygen.  Each individual red blood cell is recycled after approximately 90 days so the condition isn’t permanent but exposure to high levels of chlorine will leave the fish with reduced respiration efficiency until all affected red blood cells are replaced.  Exposure to low levels of chlorine will cause a small reduction in respiration efficiency.  Exposure to higher levels will cause greater damage and can lead to severe respiratory distress and even suffocation in well aerated water.

Chlorine or chloramine levels in UK domestic water supplies are normally in the region of 0.5 mg/L but can be raised to about 4 mg/L to sterilise the supply network, especially in advance of summer weekends when domestic water use is at a maximum.  This is particularly problematic for Koi shows since this will often coincide with the filling of show vats and spare water reservoirs.

Gill healthy
Healthy gills are blood red


Gill methaemoglobinamia
Methaemoglobinemia turns gills brown


The maximum tolerable level for chlorine or chloramine for Koi is 0.02 mg/L. This is one tenth of the value at which rapid deterioration of the respiratory system begins so, even at normal tap water chlorine values of 0.5 mg/L, exposure to undechlorinated water can often lead to fatalities.

Proprietary dechlorinators have recommended dose rates that will typically fully dechlorinate water with chlorine/chloramine levels up to 2.0 mg/L and so will provide full dechlorination at normal supply values.  However, this dose rate can only provide partial dechlorination if there is an increased level due to the higher values sometimes added by water supply authorities.

This uncertainty requires that water teams should be able to verify that water in show vats or spare water reservoirs is properly dechlorinated.

Since the maximum value of chlorine that Koi may be exposed to without harm is 0.02 mg/L measuring such low values is difficult. Cheap electronic meters that are sold on-line are unreliable, especially at low levels of chlorine.  Test strips or manual test kits are more reliable at chlorine levels higher than about 0.1 mg/L but, again, are unable to read the very low values of chlorine that will begin to affect Koi respiration.  Even expensive photometers such as the Hanna or Palintest are at their limits of accurate measurement at 0.02 mg/L and also require expensive reagents to make their tests. Fortunately there is a simple, fast and inexpensive test that will give a “safe/unsafe” result for water, either in the home pond or at Koi shows.

Properly dechlorinated water will contain no chlorine; incompletely dechlorinated water (obviously) will contain some chlorine.  Therefore, in order to ensure water has been fully dechlorinated it isn’t important to know the exact value of any remaining chlorine in the water, all that is necessary is to know that there is either “no chlorine” or “some chlorine”.  The DPD 4 chlorine test I originally developed to test purifier cartridges gives exactly that result and therefore is ideally suitable to use as confirmation that water at Koi shows has been fully dechlorinated.

DPD 4 tablets are available on-line at less than £20 for 250 [2015 prices] so the cost to a Koi show is negligible.  It’s also fast and simple so is ideal for use by busy water teams while setting up a show or while conducting water changes during the show.  All it takes to do the test is some DPD 4 test tablets, a sample tube and a piece of white paper.   The method is described below.  Clear results confirm that the water is totally free of any form of chlorine; any trace of pink indicates that the water hasn’t been fully dechlorinated and is therefore not safe to use until additional dechlorinator has been added and a second test indicates “clear”.

DPD 4 methods 150General advice for dechlorinating water
Obviously any instructions supplied with any proprietary treatment, including dechlorinators, should be carefully followed.  However, since it’s possible that some products will have a component that may settle, it’s a sensible additional precaution to give the bottle or container a gentle shake for a few seconds before dosing in order to ensure thorough mixing.

After dosing a show vat or spare water reservoir, the reaction that detoxifies chlorine is very fast and could be regarded as almost instantaneous once it is thoroughly mixed. If dechlorination is to take place soon after filling a vat then an effective way to ensure rapid mixing is to direct the filling hose at such an angle as to create a rotating vortex in the water. Another method is to add the dechlorinator into the stream of water as vats or spare water reservoirs are being filled. If either method is used then, when the correct dose of dechlorinator has been added, thorough mixing will only take a few minutes.

No precise timing can be given in this respect since it will greatly depend on the volume of water being dosed and the rate of the stirring effect. As a guide, at shows where I’m in charge of water testing, I allow five minutes after dosing a show vat and ten to fifteen minutes after dosing a spare water reservoir. These periods are far longer than is strictly necessary but are a safe practice to adopt and the test to ensure proper dechlorination can be done without further delay after these mixing periods.

The DPD 4 test method
DPD 4 tablets are available on-line for less than £15 per 100 or less than £20 per 250 [2015 prices]. Fill a standard 10 ml sample tube with the water to be tested and drop in a DPD 4 tablet. Don't look through the side in the usual fashion, place it on a white surface and look down through it. This will make it easier to see a faint colour change. If there is no chlorine or chloramine in the sample it will stay clear. The tablets begin to show a noticeable pink colour change at around 0.01 mg/L so, although this is too indistinct to be able to say what the actual level is, it is valid to say "no colour means no chlorine". If you can see the faintest pink colour in the sample, it means there is a trace of chlorine in it and there shouldn't be.

Strictly, a DPD 4 tablet doesn’t just test for chlorine, it is also looking for any other oxidising reaction, so, although it provides an instant colour change when any form of chlorine is present, it will then very slowly produce a pink colour change due to dissolved oxygen.  This is especially noticeable if the sample is left exposed to the air so that more and more oxygen can enter the solution. Look for the colour change immediately because even if there is no immediate pink colour, showing that there is no chlorine in the sample, after several minutes dissolved oxygen will begin to turn it pink anyway.

Additional information about types of DPD 4 tablets
There are two types of DPD 4 tablets. The "Rapid Dissolving" tablets do exactly that but the ingredient in the tablets that causes them to rapidly disintegrate and dissolve results in them tinting the water white. They still turn the sample anywhere from pale pink if there is a trace of chlorine or chloramine present to deep pink if there is a lot of it present.

There are also "Photometer Grade" DPD 4 tablets which are a little more expensive. These are difficult to dissolve but they leave the sample totally clear unless there is any form of chlorine present. Don't shake the sample tube vigorously in an attempt to dissolve these types of tablets; that will dissolve oxygen into the sample and may cause a false positive reading. The tablets should be crushed in the bottom of the sample tube with a specially made tablet crusher or with something that resembles the blunt end of a plastic knitting needle. After that, a couple of inversions of the tube will be all that is necessary to ensure good mixing.

Both tablets react identically to chlorine/chloramine the only difference is that the rapid dissolving types add the white tint in addition to any pink colour change due to chlorine, whereas the photometer grade tablets leave the sample clear except for any pink colour due to the presence of chlorine.

Chlorine or chloramine affects haemoglobin in red blood cells making it incapable of transporting oxygen around the body.

  • The amount of red blood cells affected will depend on the level of chlorine present and the length of exposure.
  • If a significant percentage of haemoglobin is affected, the respiratory process will become so inefficient that fish can suffocate, even in well aerated water.
  • Damaged red blood cells are naturally recycled after a maximum period of about 90 days so, if an affected fish doesn’t die soon after exposure and it can be kept in highly aerated water it will slowly begin to recover and can be expected to be fully recovered after 90 days.
  • Dechlorination should be done in strict accordance with manufacturers’ instructions but it’s a wise precaution to give bottles or tubs a gentle shake to ensure that the dechlorinator is properly mixed in its container.
  • To ensure thorough mixing of dechlorinators into vats, add them into the stream of water whilst filling or into the rotating vortex in a newly filled vat.
  • The DPD 4 test, described above, is an instantaneous indicator of “complete dechlorination” or “insufficient dechlorination”.
  • The method is simple, inexpensive and provides an instant result but must be done as described for the results to be valid.
  • Look down into the sample onto a white surface since this will make a faint colour change easier to see as the depth of water in the sample tube will effectively multiply any colour change by a factor of about ten.
  • The test doesn’t require any developing time so look for any colour change as soon as the DPD 4 tablet has dissolved.
  • No pink colour in the sample indicates no chlorine i.e. dechlorination has been totally effective.
  • Any trace of pink in the sample indicates that a trace of chlorine remains i.e. total dechlorination has not been achieved and that additional dechlorinator should be added.
  • Don’t delay looking for a colour change since, if the sample is left exposed to the air for several minutes, oxygen will dissolve into it and will slowly turn pink anyway.
  • Procedures at different Koi shows will vary but a sensible addition is to appoint one person as being in charge of testing that all vats are properly dechlorinated and ensuring that a label or other visual indicator is affixed to spare water reservoirs which will indicate that they are safe to use for water changes.

Additional details of the test method are in the section Manky Sanke Explains on this link:
DPD test for chlorine


DPD4 chlorine test02