The Velvet disease
may be latent in the aquarium waiting for favorable conditions to attack, like the abrupt changes in the temperature of the water or the weakness of the fish.The parasite can enter the aquarium through new sick fish, or through objects or plants with spores. Hygiene and quarantine periods should be adopted as mandatory before putting fish or objects into the aquarium.
In the case of decorative objects, rocks or plants, clean them with a disinfectant or boil them during twenty minutes will be enough.
As preventive measure they can also be placed in a quarantine tank during one week, enough time so that any spore dies before finding a fish to parasite.
The replacement of water should be made with water at the same temperature of the aquarium water, because the abrupt changes in temperature affect the fish
Some species of the parasite also obtain energy through photosynthesis, therefore cover the aquarium can help to weaken the parasite. The most common treatments against the velvet disease
are based on copper salts, but it is not always advisable because not all the fish tolerate the copper.
Alternatives are the salts of quinine or blue of methylene. Increase the water temperature to 82-84 F can help to the treatment, since it accelerates the biological cycle of the parasite.
p/s remove any carbon filters in the tank until the fish is ok