Methylene Blue

Butterflyfish swimming above coral in an aquarium
T. Nakamura Volvox Inc. / Getty Images

Methylene Blue (also known as Methylthioninium chloride) is a cationic dye, redox indicator, and photosensitizer. In aquaculture, it serves as an anti-fungal and anti-parasitic and has commonly been used to treat fish eggs to ensure they are not lost to fungal overgrowth. Methylene Blue is an aquarium-safe disinfectant and can also be used for the treatment of ammonia and nitrite poisoning.

Uses

Disorders that Methylene Blue is used to treat include the following:

  • Nitrite Poisoning: Fish gasp for breath, tan or brown gills, rapid gill movement known as "gilling."
  • Ammonia Poisoning: Fish gasp for breath, red or purple gills, lethargic - may lay on the bottom, red streaks on body or fins.
  • Ichthyophthirius Multifilis: Small white spots resembling sand, fish scratches against objects.
  • Oödinium Pilularis: Also known as Velvet, this is actually caused by a parasite.
  • Swim Bladder Disorder: Fish struggles to maintain proper position, floats upside down, swims with tail higher than the head.
  • Egg Fungus: Serves as a safe and mild disinfectant for fish eggs.
  • Fish Stress: Prophylactic treatment of fish under stress, usually due to being moved.

Safe Applications

Methylene Blue can be used with crustaceans, including crabs, shrimp, and snails, but should be introduced carefully. It will damage live plants and should be used with caution in such cases, ensuring that plants are exposed for only limited periods of time.

Methylene Blue should not be used concurrently with Erythromycin or Tetracycline. After using a Redox reducing type of water conditioner (which includes most water conditioners), wait for 30 minutes before adding Methylene Blue. Discontinue the use of carbon media in filters while treating, as it will remove the Methylene Blue.

Methylene blue dissolving in water
 

Fungus on Fish Eggs

For prevention or treatment of fungus on fish eggs, follow these instructions for treating your aquarium with Methylene Blue:

  1. Remove carbon from the filter and continue to operate with mechanical filter media.
  2. Add 1 teaspoon of 2.303% Methylene Blue per 10 gallons of water. This produces a concentration of 3 ppm. For increased concentrations, add approximately 1/3 teaspoon (1.64 ml) per 10 gallons for each required 1 ppm increase.
  3. Only one application is needed. Treatment should continue for 3 days past the free-swimming stage or for livebearers 2 days after birth.

External Parasitic Protozoans

If your aquarium is affected by a fungus or by external parasitic protozoans, apply Methylene Blue using the following steps:

  1. Remove carbon filter and continue to operate with mechanical filter media throughout the treatment period.
  2. Add 1 teaspoon of 2.303% Methylene Blue per 10 gallons of water. This produces a concentration of 3 ppm. Continue the treatment for 3 to 5 days.
  3. Make a water change as noted and replace the filter carbon at the conclusion of the treatment.

Nitrite or Cyanide Poisoning

As an aid in reversing nitrite (NO2−) or cyanide (CN−) poisoning of marine or freshwater fish, use Methylene Blue in the following application:

  1. Remove carbon filter and continue to operate with mechanical filter media throughout the treatment period.
  2. Add 1 teaspoon of 2.303% Methylene Blue per 10 gallons of water. This produces a concentration of 3 ppm. Continue the treatment for 3 to 5 days.
  3. Make a water change as noted and replace the filter carbon at the conclusion of the treatment. parasite protozoans."

Use as a Dip

You can also use Methylene Blue as a dip for treating fish with fungal infections, those affected by external protozoan parasites, or those suffering from cyanide poisoning.

  1. Prepare a nonmetallic container of sufficient size to contain the fish to be treated by adding water similar to the original aquarium.
  2. Add 5 teaspoons (24.65 ml) per 3 gallons of water. This produces a concentration of 50 ppm. It is not recommended that the concentration is increased beyond 50 ppm.
  3. Place fishes to be treated in this solution for no longer than 10 seconds.
  4. Return fish to the original aquarium.

Products

Fish Vet Methylene Blue 

Dosing Instructions: 1.25 oz. dropper bottle dosing instructions: Add 1 drop per 1 gallon. Perform 25% water change after 3 to 5 days and replace carbon. If used as egg fungal preventative continue treatment 2-3 days after fish are free-swimming.

Powdered concentrate dosing instructions: Remove top and slowly add water to the top of the bottle. Replace cap tightly and shake gently to mix (we recommend using Reverse Osmosis or Distilled water). Add 1 teaspoon per 10 gallons. Perform 25% water change after 3 to 5 days and replace carbon. If used as egg fungal preventative continue treatment 2-3 days after fish are free-swimming.

Discontinue carbon filtration but keep all other filtration running during treatment. Replace carbon after treatment.

Kordon / Oasis Methylene for Aquarium 

Manufacturer's Directions for Use: The following procedures are suggested for freshwater and marine aquariums and ponds. Methylene Blue can be absorbed by porous materials such as rock, coral, and wood. The product is best used in bare aquariums or ponds, especially if they are new. Methylene Blue may permanently color the silicone sealant in aquariums. At the conclusion of all treatments, a partial or complete water change should be made and activated carbon replaced in the filter.