Both Lom (1995) and Noga (2000) recommend formalin baths of between 0.125 and 0.167 mL/L for 30 to 60 minutes. The warmer your water, the less formalin that should be used as both formalin and increasing temperature reduces the oxygen saturation of the water.

The bath water should be matched closely with the tank water and probably the best way is to take water from the tank and place it in a bucket, add the formalin. mix well and treat the fish. Replace the removed water with fresh seawater (artificial or natural depending on what is normally used). Add an airstone to the dip bucket to ensure good aeration (and then toss the airstone away). After the dip is completed, dilute the dip water with 4 times the volume of tap water and discard.

To each gallon (or 4 litres) of bath water, around 0.6 mL of formalin should be added to get the desired dosage.

Have a second bucket of tank water ready to transfer the fish to when the treatment is complete or the fish shows signs of stress. The second bucket allows the fish to be "rinsed" before it is placed back into the tank.

Don't use formalin if the water temperature is greater than 27°C (80°F).

See also:

Formaldehyde: Friend or Foe? by Terry D. Bartelme

References

Lom J. 1995. Trichodinidae and other ciliates (Phylum Ciliophora) In: P T K Woo (ed.) Fish Diseases and Disorders. Volume 1: Protozoan and Metazoan Infections. CAB International, Wallingford, Oxon. pp 229-262.

Noga E.J. 2000. Fish Disease: Diagnosis and Treatment. Iowa State University Press, . 367pp.

Last updated: May 8, 2004