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Methylene Blue in Aquariums

Methylene Blue is an medicine used in aquariums for fungal and bacterial infections.  It is also used for parasite infestations.

Methylene Blue is also effective in treating fishes which have been exposed to nitrite poisoning.  Nitrite is a poisonous product produce by decomposing waste in the aquarium.  It is broken down into harmless nitrate compounds. 

However, if the water is not replaced at regular intervals or if the biological filter is not working, the nitrite levels can spike.  And fish can become sick.  Such fish can be kept in a bath of methylene blue.  Methylene blue increases the level of haemoglobin the blood of fishes, increasing the ability of blood to carry oxygen. 

Methylene Blue usually comes in a liquid form or in the form of a powder.  Follow the instructions in the bottle. 

General Dosage
Bath: 12 mg per litre.  Keep the fish in the solution for 10 minutes

Dip: 50 mg per litre.  Keep the fish in the solution for 10 seconds

It is better to add the medication to a separate quarantine tank and introduce the sick fish into it.  This is because methylene blue is indiscriminate.  It also destroys the beneficial nitrifying bacteria which can result in ammonia spikes.  Methylene blue will also result in a blue stain on the aquarium. 
Methylene Blue is also toxic to plants.   Do not add methylene blue to the aquarium, if you have live plants.

If you want to add the methylene blue to the entire aquarium, consult your veterinarian.
In some situations, methylene blue may not totally the infection or the parasite infestation.  In such cases more specific medication may be required. 

Methylene Blue while Breeding
Methylene blue is also used when breeding fishes.  Fish eggs are particularly prone to fungal infection.  Keep the breeding pair in a separate tank. Add methylene blue to the water.  this protects the eggs from the fungus.