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Methylene Blue



Methylene Blue comes as a very dark green powder, appearing blue when dissolved in water. Considered a 'traditional' medication for bacterial, fungal and parasitic infections, it is used less frequently as it is highly toxic to plants and will wipe out the bacteria in a biofilter. It is easily absorbed through cell membranes and affects cell activity by raising oxygen consumption within cells. The therapeutic action of Methylene Blue on bacteria and other parasites is probably due to its binding with cytoplasmic structures within the cell and also its interference with oxidation reduction processes 



Methylene Blue, although considered as a 'traditional' medication, is for a variety of reasons useful to Koi keepers. One of the main uses is for the reduction and spread of bacterial and fungal infections on fish eggs. When treating Koi, Methylene Blue can be employed against ich, skin and gill flukes, funguses, velvet (Oodinium) and most other external parasitic and infectious diseases. Although there are far more effective medicines for actual treatment of these pathogens, Methylene Blue remains a valuable part of the Koi keeper’s arsenal of medications when caring for koi. The reason is obvious when one studies the ingredients of many off the shelf medications for Koi. Methylene Blue remains the main ingredient of many medications. Whether the Koi Keeper uses Methylene Blue or medication that consists mainly of Methylene Blue it will be valuable to understand the effectiveness, advantages and disadvantages of it.

Methylene Blue can be safely mixed or added to other dip/bath compounds, while it still remains effective. It is also very effective when used as part of a "medicated fish bath" for treatment of ammonia, nitrite, and cyanide poisoning as well as for topical and internal treatment of injured or sick fish as a "first response". In fact, Methylene Blue converts methemoglobin to useful hemoglobin, reversing the ill effects of nitrite and even cyanide exposure. The anti bacterial efficacy of Methylene Blue was found to be higher for gram-positive bacteria than for gram-negative bacteria. It is a good oxygenating dye. The properties of the drug as an oxygen transporter, similar to our blood’s hemoglobin, assist in keeping oxygen concentration in water high. It is also helpful in reducing light penetration and soothing frightened livestock.

In view of the above, the most useful application for Methylene Blue is during transportation of Koi. The addition of Methylene Blue to transportation water increase the oxygen carrying capacity of the water, it also kills bacteria as well as certain parasites and is relatively non-toxic in a very wide range of concentrations. Adding Methylene Blue to transportation water is a very good initial step in the quarantine process.

A study was recently conducted in the Philippines to determine the effect of sodium chloride (Salt) and Methylene Blue on the bacterial load in the transport water while transporting Nile tilapia. Of interest here are the results obtained with Methylene Blue.

Transport bags were treated with two dosages of Methylene Blue. Treatment one consisted of 3 mg/l of Methylene Blue (This dosage was based on literature). Treatment two was done at a dosage of 1 mg/l of Methylene Blue (based on farm practice). Each treatment was replicated three times.

In this study, Methylene blue and sodium chloride were found to be effective in reducing the bacterial load during transport. Furthermore, no significant difference between concentrations of Methylene blue based on literature and on farm practice was observed.


As proven in the study mentioned above, accurate measures are not really necessary, as Methylene Blue is safe and effective over a wide range of concentrations. Most dealers and hobbyists buy a Methylene Blue solution from dealers and just ad enough Methylene Blue to the water to make it very blue.


Methylene Blue may permanently stain nets and silicone piping. It is therefore not useful as a disinfectant for nets/equipment.

Methylene Blue is toxic to aquarium/pond plant life

Methylene Blue should not be used for prolonged exposure, or in permanent (main, display) systems, as it can/will kill off necessary beneficial bacteria.

The effectiveness of Methylene Blue is reduced by suspended/dissolved organics in the water

Last Updated on Wednesday, 29 February 2012 12:51