Its best to talk to other hobbyists and get recommendations on how the fish you are interested in is compatible with the fish you already have in your tank.

There are thousands of possible combinations, so trying to cover them all here is impossible.

Forums are a great source of advice

Visit one of the forums like www.ReefCentral.com and many people there will be glad to help you.Always try to get advice from several people who actually have tanks! Surprisingly, lots of people want to give advice about things they don't know much about first hand. Experience is king when you are getting advice!

Find out the compatibily of the fish you want BEFORE you introduce it in your tank. Its really sad to see a fish cowering in the corner and being beat up by its tank mates. If the new addition is not compatible, you might just have to tear down your tank to get that new fish out before one of your other fish kills it.

Observe how the pet store has the fish. Are they together in a group of the same types? Or is each specimen of the same fish in a different tank. That would indicate that you shouldnt put two of the same together.

Certain fish, such as our favorite, the yellow tang (Zebrasoma flavescens) are very docile and almost always not aggressive towards other fish. And they have the added benefit of doing something good for you tank. Tangs are great and helping keep hair algae undercontrol. For more on this, see our section on Best Fishes for Algae Control.