Methylene Blue

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Methylene Blue

July 29, 2018 - 15:55

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.


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.

By: Chris Neaves

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