Potassium permanganate

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What is it

Potassium Permanganate container.jpg

Potassium permanganate (PP) is a compound that is used by aquarists for the disinfecting of plants or ornaments before placement into aquariums. It is used to remove organic build-up in tank water, and kill bacteria and fungi. It is also employed to treat some parasites that infect fish.

Potassium permanganate is the chemical compound KMnO4. The salt is also known as "permanganate of potash" and "Condy's crystals". The permanganate ion is a strong oxidizing agent. It dissolves in water to give deep purple/pink solutions, evaporation of which gives prismatic purple-black glistening crystals (see picture below).

Plant disinfecting

To prepare for the disinfecting of aquatic plants, prepare 1 Litres (0.3 US G.) of lukewarm (25°C (77°F) ) clean tap water and drop 10 mg of crystals into it and stir until the solution turns deep blue/purple.

Be careful as this solution will stain and is toxic to life.

Dip the leaves of the plant into the solution for 10 minutes, being careful not to dip the roots of the plant in it.

Then rinse off thoroughly.

This will kill live snails as well as snail eggs and parasites [1].

Fish treatment

Potassium permanganate can be used to treat parasites on individual fish. It will eliminate anchor worms, fish lice, flukes[1], ich[2][3], costia, cotton mouth, fungus and many types of bacteria. Prepare 8 Litres (2.1 US G.) of water at aquarium temperature and add 1/8 teaspoon (0.6g) of crystals.

Tank treatment

Potassium permanganate is an effective anti-parasite treatment (Ich, etc.), as well as being able to remove odours from tanks and increasing the redox potential of the water.

However as this compound is very toxic, using the wrong dosage will result in killing all life in the tank. Please read this excellent article on how to get the safe dosage on FishDoc.co.uk.

Removing odours

The build-up of odours in old aquariums is caused by the decay of organic material.

You need to prepare a dosage of 0.5ppm of PP. This is 0.065g per 200L of water to give you 0.5ppm in solution.

0.065g of PP in 1L of water will give you a 100ppm solution. So using 5ml of this solution per 1L of water will give you a 0.5ppm level.

To reduce the smell, place the crystals into a small clear container and add 1L of warm water (preferably distilled or deionized water). Stir carefully until the water is deep purple and the crystals are fully dissolved from the bottom. Then using great care add 5ml slowly into your aquarium and repeat. Stop adding as soon as you see the overall tank water stained very light pink. A 30 Litres (7.9 US G.) tank may only require 5-10ml.

Switch off the tank lights (Potassium permanganate rapidly becomes neutralised in light) and ensure the tank is well aerated for the next 12 hours. Turn on the lights briefly once an hour to monitor the water colour (don't be surprised if the light pink colour has gone) and the to monitor the fishes reaction (if they are gasping for air you will need to add more aeration or do a water change). Don't apply any more for a further 12 hours. Reapply after 24 hours have passed from the initial dosage if required.

Alternate solution

Simply engage in regular partial water changes, and use fresh activated carbon in your filter(s).



  1. 1.0 1.1 The Skeptical Aquarist
  2. Potassium Permanganate Kills Fish Parasite - USDA
  3. Ichthyophthirius Multifiliis (White Spot) Infections in Fish - University of Florida IFAS Extension
  4. Potassium permanganate on FishDoc
  5. Potassium permanganate - by Doc Johnson

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