Potassium permanganate In its raw state, potassium permanganate is an odourless dark purple granular or, in some blends, crystal powder.  It is primarily an oxidising agent with disinfection properties. Its chemical formula is KMnO4 and, years ago, it was often referred to as Condy’s Crystals Keeping koi safe Potassium permanganate has been used in koi keeping for many years and, as a generic substance, it should always be open to debate.  Such substances have not been fully investigated and their current role in pond treatment is based on their historical use.  It is important that we discover more about their properties and safety and this article outlines the findings of research carried out in my laboratory on potassium permanganate use in koi. Monitoring koi during research Changes take place in fish after any chemical treatment and, if they continue to behave normally, the conclusion is that no adverse reaction has occurred. In reality, there is always some reaction, even if minor, that is unobservable by koi keepers.  With laboratory facilities and simulated conditions, we can detect even small changes and study koi as they go through various stages after exposure to any substance.  We can see the response in each layer of the epithelium or skin to the treatment product as well monitor the major organs.  We are also able to calculate the time scale required for fish to return to the physiological state they were in before exposure to the substance. Assessing results In looking at the changes that potassium permanganate triggers in koi, we have to see if there is improvement in the condition under treatment. In addition, we have to assess any negative side effects and conclude if they are detrimental at a level that prevents recommending its use.......  On the other hand, we must consider if there are certain applications for which it is still appropriate as no other product is available for that specific purpose. In any investigation of this type, we ensure that the koi are not at any risk and are not stressed by examinations. Results It was found that the epithelium, or skin, in koi undergoes various changes when exposed to potassium permanganate.  The mucus layer is removed from the cuticle, the term for the area covered by mucus. From that point, the capacity of the goblet cells to regenerate the mucus at the normal rate is impaired. As the first part of the immune system, mucus contains proteins to defend the body and during disease it traps and sloughs off harmful microbes that land on the skin.  Our project found that, after exposure, many of the proteins found in healthy mucus were either not present at all, or were found at a very low level.  Another highly significant result in this investigation was the fact that the koi exposed to potassium permanganate became predisposed to bacterial disease.  Whilst our project was limited to the common bacterial pathogens found in koi ponds, we can assume koi could be equally compromised by other disease causing agents.  The fish remained unprotected even when the mucus eventually regenerated and this phase continued until the normal proteins were present in the mucus. This delay varied from fish to fish and, in many koi, it was over 6 weeks before a degree of normality was restored in the mucus layer. Conclusion Potassium permanganate raises concerns in the treatment of koi and, in my opinion, should not be used in any situation when an alternative treatment that is known to be safe and effective is available. For example, there are several anti bacterial products on sale such as chloramine T or acriflavine so there is no need for reliance on potassium permanganate if waterborne bacteria is suspected. Trichodina is a free living organism not a true parasite and it can be stubborn to treat.  Potassium permanganate is frequently recommended to treat Trichodina and this could lead to koi being over exposed. It will take time The LFH research project is ongoing and we will not only investigate potassium permanganate, other generic substances are being assessed.  We have passed our findings on to various interested parties and, as yet, our conclusions are not widely known although concern has been noted.  Chemists working in aquaculture have been approached, however, koi are a small sector of the aquatic industry and product development is not always financially viable. LFH have agreed to carry out trials should any alternative product become a reality to minimise costs.  Potassium permanganate remains legally on sale in the UK and there will be advocates of its use for some time to come.  I am simply sharing our results with koi keepers, encouraging the development of safer products, and advising caution in the use of potassium permanganate.