Velvet or Rust Fish Disease
The Velvet or Rust fish disease is a very common and particularly common to bettas (Siamese fighting fish).
Ultimately if your freshwater fish looks like it has been sprinkled with gold sparkles like you had when you were a kid during arts and crafts, it probably has velvet or rust fish disease.
Velvet is a health issue that is caused by a parasite that attaches itself to the fish and then falls off after a week or two. When they fall off your aquarium fish into the substrate they immediately begin to aggressively multiply. The new born velvet parasites are released into the water and then re-infect your fish. The interesting fact is if the parasite can not find a fish to land on for a few days they die. That is how you are able to treat the fish very easily.
The best remedy for velvet is malachite green. Malachite green is found in any pet store. You can also add 1 tablespoon of aquarium salt for each 5 gallons of water. I must stress “aquarium” salt. DO NOT use table salt.