Ammonia Problem I Think
One of the fish turned black on its fins and tail. We corrected the problem and I think the fish is a little more frisky but the other fish in the tank, is still trying to bite it.
Should I isolate the sick fish?
For those that don't know, goldfish that have been injured, or sickness has caused damage to the fins or skin, the areas affected will turn black.
The black coloration indicates that healing is taking place.
This only applies to metallic scaled
fish. Matts and calicos (nacreous) don't go through a color change like metallic scaled goldfish.
Over time, the black coloration will fade and the fish will return to its normal coloration.
Rule number one with sick goldfish, or any sick fish, is to isolate.
The three reasons are:
1. Stop the spread of the disease
2. Enable treatment using chemicals at a strength that may kill other types of fish or plants in your aquarium/pond
3. Stop other fish picking on the sick individual. This seems a common practice amongst many different species of fish.
You are correct that ammonia will cause damage to finnage, usually showing up initially as whiteness around the edges caused by burning.
Ammonia build up is caused by excessive waste in the water, which is a problem with goldfish. This is why a filter
is almost mandatory for goldfish.