Maracyn-two By Mardel

Wipes out bacteria in no time flat. The BEST choice if fish become ill. Nothing else works like Mardel. Maracyn-Two is a must have for fish emergencies. Includes the fantastic symptom guide.

Pros: Cures disease, easy to use, non-toxic

Cons: Expensive, can take a lot to treat large tank

Maracyn II is one of the best all around Meds to keep handy in the house for sick fish.
I have used this on more than a few occasions,and have never had any problems with it.
If you're not sure whats wrong with your fish,and you've checked for water probs,then Maracyn II is safe enough to go with.

Pros: It combats a lot of different diseases

Cons: Can get quite costly in big tanks