Using Formalin
Formalin is a chemical that is derived from a 37% solution of formaldehyde and water containing 10% to 15% methanol, which inhibits formation of paraformaldehyde , a highly toxic compound. It is a known carcinogen and should be handled accordingly.
Formalin is effective against most external parasites and some fungi; it is not effective against bacteria of any kind. It is excellent for killing gill flukes. In an aquarium the usual dosage is 25 ppm. You can obtain this by adding 2 drops per gallon or 1 ml per 10 gallons of water. When dosed this way it can be used for extended periods of time but 3 days is the norm. Whenever using Formalin it is important to provide as much water surface movement as possible since Formalin will reduce dissolved oxygen in the water column. Higher temperature fish, such as discus, need to be watched closely for both lack of O2 and because Formalin is more dangerous at higher temperatures.
Formalin/Malachite Green
Use this much the same way as you would Formalin alone. This is the recommended treatment for two reasons
- It’s readily available, this is what almost all Ich medicines are formulated from
- The Malachite Green will help against secondary infections such as bacteria
Dose this as per the manufacturer’s instructions for no less than 3 days. Do at least a 50% water change between dosing and replace only what FMG was taken out. With the water change.
Formalin is very safe if not abused by over-dosing and enough oxygen is provided by surface agitation or an airstone.