Ich/White Spot: This is probably one of the most common fish diseases. Ich looks like literally white spots all over the fish. This is a Protozoan disease caused by Ichthyophthirius in fresh water aqauriums (Cryptocarion irritans in Marine). It is a parasite that attacks the eyes, fins, gills, skin and mouth interior.
Symptoms: White spots all over the fish. The fish may attempt to scrape itself against objects in the aquarium, have a loss of appetite or a stressed-rapid breathing. The parasite can only be affected by treatment during the free-swimming stages of the cycle.
Treatment : A Copper Sulfate or Copper Formalin medicine should be able to kill most infections. There are many medicines all do the trick.

If the fish are salt tolerant give your fish a salt bath. Also raise the temp this ups the life cycle of the disgusting parasite.