Fin rot is a bacterial infection which affects freshwater and saltwater fish.  Goldfish seem to get fin rot more than any other fish.

Fin rot will make your fish look as if the fins are torn and split.  The fins will also start to disappear right off of the fish. 

Fin rot is very hard to get rid of.  If you want to avoid fin rot you need to check your fish daily for signs of fin rot.

Fin rot is often times caused by:

Poor water quality

Overcrowding

Overfeeding

When fish get stressed out, their immune systems will be lowered down to virtually nothing.  This is when the fish get sick.  When you overfeed and overcrowd your fish there is excess food which decays in tank.  There is also extra fish waste in the water which raises the ammonia level.

To keep your fish from getting sick, change the water at least once every 2 weeks.

You will want to treat your fish as soon as possible.  You can purchase the medication from your local pet store.

You will want to raise the temperature to around 84 degrees.   You can also purchase freshwater salt to give your fish a saltwater bath.  Add the recommended dosage of salt which is stated on the box.

You will need to treat the water and the fish.  Remember to remove the filter cartridges because the carbon will remove the copper from the water.