Sailfin Tang swimming vertical and loosing color

[guystran]

I have a fish-only 20 gallon saltwater tank. It has been running for about 6 months with 2 clown fish and 2 damsels. Yesterday I added a sailfin tang that I have had my eye on since I started my tank 6 months ago. I know 20 gallon tanks are not recommended for a lot of fish. The tang was going to be the last fish I add to this tank until I step up to a larger tank. When I put it in the tank last night it was swimming funny almost like it was dying. Today it was completely vertical and it lost the majority of its color. I went to net it out and it started swimming around but the same as last night. Now its still vertical and floating around the tank. I was thinking at first it may just be in shock and it will pull through but now I don't know and I really don't want to loose this fish. Any help will be appreciated.

UPDATE:
I read online that tangs need an oxygen rich tank so I added an airline to my power head and a air stone bar. The tang is still acting the same way just floating through the tank with little movement and looks red under the gills.

[leebca]

The 20g tank should have only one of those four Damselfishes you currently have in it (Anemonefishes are Damselfishes). A Tang of any size doesn't belong in that sized aquarium at all. A 20g FO or FOWLR tank is a bit of an oxymoron -- that tank is best suited to one fish in a nice reef setting. If you really would like to keep the assortment of fishes you currently have in that tank, you begin with a long 125g aquarium.

The Tang is most likely suffering from an acclimation problem. Most die once they have reached this condition. You may have one that actually survives, however. Not anything to be done. Should it pass, please don't replace it and find homes for some of the other fishes.

Good luck!