Background

Velvet, or Oodinium, much like Ich, will take over an entire goldfish tank within a few days. Typically introduced to the tank by unquarantined new goldfish, options to prevent Velvet are:

• No new goldfish
• Quarantine a new goldfish properly before adding them to the tank.

Diagnose

Velvet symptoms can include:

• Flashing and scratching
• Thick slime coat
• White-yellowish patches on the skin 

Treatment

While salt is usually a common cure, in the case of Velvet salt will do almost no good. However, any medication containing Formalin for a period of three days should do the trick. Similarly copper can help, but can be bad for the goldfish.