Potassium permanganate and fish disease
Potassium permanganate is a useful fish disease treatment; acting
against a range of protozoan parasites including Trichodina, Costia and
Chilodonella, as well as monogenean flukes Gyrodactylus (skin
flukes) and Dactylogyrus (gill flukes). In addition to
being an effective anti-parasite treatment, potassium permanganate can
also assist with bacterial gill disease and bacterial disease such as
skin ulcers. It will also oxidise dissolved organic matter, reducing the
biological oxygen demand and improving water quality and clarity. All
sounds too good to be true!
With regard to ornamental fishponds, it is mainly used in koi ponds
because of dosing difficulties in heavily planted ponds.
Effective against Trichodina
My own experience is that in most cases it is very effective against Trichodina,
clearing the problem quickly. Against this particular parasite it would,
in most circumstances, be my first choice. I have had mixed results
against flukes and Costia, but this is possibly due to the excess
mucus often produced by these parasites providing protection.
A powerful oxidising agent.
As with many disease treatments, potassium permanganate is not really
a medicine. It is a caustic alkali that, at high doses, can cause
serious corrosion of delicate tissues such as skin and gill. In ponds it
works as an oxidising agent in a similar, although milder, fashion, to
household bleach! It is a very reactive chemical, reacting with organic
a powerful oxidising agent
Oxygen is usually
seen as a benign substance. However, oxygen atoms - as released
in some oxidising reactions - are extremely reactive. One common
reaction involving oxygen is fire and fireworks. A slower, but
just as destructive reaction is rust, in which iron is oxidized.
agents should be used with extreme caution - double and
treble-check the pond size and calculated dosage.
During such reactions the manganate ion, MnO4- loses
two oxygen atoms and is reduced to insoluble manganese dioxide MnO2.
The ‘lost’ oxygen atoms react aggressively with other organic
molecules, altering their structure and properties. It is these reactive
properties that kill bacteria and parasites such as Costia,
Trichodina and flukes.
Although it is a very useful disease treatment, its reactiveness with
organic material can make it a difficult and potentially dangerous
treatment to use. It will react readily with any organic matter. If the
pond has any particulate organic material, such as algae, detritus, or
dissolved organic compounds, then much of the oxidation reaction will
take place with these organics rather than the parasites or bacteria we
are targeting. For this reason potassium treatments will not be
effective in green water.
Therein lays a major problem with its use. We need to calculate a
dose that will leave an appropriate residue (1.75 mg/litre) of unreacted
manganate ion after any such reactions. It is only this residual level
that will be effective against bacteria and parasites such as Costia,
Trichodina and flukes.
Clearly, the level of dissolved and particulate organics will vary
considerably from pond to pond - dependant on many factors. If the pot.
perm. residual level is too low then the treatment is liable to be
ineffective. If, however, the residual level is too high, then it is
likely to be harmful and possibly fatal to fish.
There are two methods to calculate the required doses.
The first is to calculate the organic
level of the pond water by adding 0,1,2,3,4,5,6,8,10 mg of
pot.perm. to separate one-litre containers of pond water (plastic
bags will do). After 20 minutes see which is the lowest
concentration still retaining a very faint pink hue. (Or
alternatively add successive 1 mg doses at 20 minute intervals to
the same litre of water until the water just stays faintly pink.)
If the lowest concentration that just stayed pink were, for
example, 2mg/l, then the appropriate pond dosage would be 2 + 1.75
= 3.75 mg per litre. This method does depend on very
accurate measurements. To aid accuracy, a stock solution of one
gram per litre could be used, giving 1mg potassium permanganate
The alternative is to treat the pond with 2 mg pot. perm. per
litre. If it retains a pink hue for 4- 6 hours then the dosage was
probably OK. If not, re-dose the pond the following day with 1.75
mg/l and repeat this daily until such times that it does retain a
pink hue for 4 - 6 hours. You should not add more than a total of
6-8 mg to a pond during any course of treatment. If these
levels are needed, then clearly the organic level is too high and
needs to be reduced by pond cleaning and/or water changes before
More about potassium permanganate
Biological filtration systems should be isolated during
treatment, as bacterial flora will be adversely affected.
Repeated treatments may result in cumulative gill damage
It is affected by sunlight, so treatments are best carried out
in the evening, or on cloudy days.
It is best to give the pond a good clean and vacuum before
treatment to reduce the amount of organic matter.
It is is more toxic at higher pH. In alkaline conditions a
solid precipitate of manganese dioxide (MnO2) can form
on gills. This can cause respiratory problems by blocking the
gills. Additionally, MnO2 is a strong oxidising agent
and presumably in such a situation could cause other gill-tissue
Its use against bacterial gill disease has to be balanced
against the possibility of further damage from the treatment. It
will assist by killing bacteria and parasites in the gills.
However, in such situations the gills are often swollen and
congested and if a manganate precipitate does form on the gills it
could push the fish over the top. This is more likely in alkaline
conditions. It would not be my first treatment of choice for this
condition unless there were serious parasite complications.
It should not be mixed with formalin as this produces toxic
It can be neutralized by adding hydrogen peroxide. A
recommended level of one litre of 3% hydrogen peroxide (mixed in
10 litres of pond water) will deactivate 20,000 litres of treated
pond water. I have been using just 150 mls. of 9% hydrogen
peroxide (available from drug stores) per 20,000 litres pond water
to neutralise remaining potassium permanganate residues at the
conclusion of treatments. This quickly clears the murky brown
water, leaving the pond crystal clear. If too much hydrogen
peroxide is used the unreacted residue action may prevent further
potassium treatments for a day or two, so it is best to only use
hydrogen peroxide at the conclusion of a treatment. If the water
gets too murky between treatments (as would happen with a high
organic content), hydrogen peroxide could be used to clear the
water but it would be advisable to do a good water change before
It is effective against smaller ectoparasites such as Costia,
Trichodina and Chilodonella however its
effectiveness against larger parasites such Gyrodactylus
(skin flukes) and Dactylogyrus (gill flukes) is
dosage dependent. At residual doses below 1.5 mg/litre, treatments
against flukes are not likely to be effective. Short-term bath
treatments at higher doses are liable to be more successful.
It can be a useful support treatment when treating bacterial
ulcers; first by reducing any parasite load and secondly by
reducing both the organic content of the water and the bacteria
levels. Although it will assist in the healing process, it will
not, on its own, cure ulcers.
Wear gloves when using potassium permanganate as it will
quickly react with the skin leaving a nice deep brown colour that
looks as if you smoke about 100 a day!
Pond or tank treatments: residual 1.75
mg / litre. Effective against bacteria and parasites
(not larger parasites such as Lernaea or Argulus ).
Can be repeated every 2-3 days – maximum 3 treatments.
Short term baths: Effective
against bacteria and parasites (not larger parasites such as Lernaea
or Argulus ). Can be repeated daily. Maximum 5
Dips: - 20 mg / litre for 20 seconds. Said
to be effective against Lernaea or Argulus Dips can
also assist in stubborn parasite cases. Only use as a last resort.
See the fish disease section for more details about
specific parasites or diseases
i.e. 5 ppm = 5 mg / litre
mg / litre x
3.785 = mg / gall
i.e 5 mg / litre = 18.9 mg / gall (US)
mg/ litre x 4.546 =
mg / gall
i.e 5 mg / litre = 22.7 mg / gall (UK)
To convert imperial
gallons to US gallons multiply by 1.2
1 ounce = 28.35 grams
1% solution =
10 ml per litre
10 gram per litre
38 gram per
45 gram per gall