Sigh
Ok-- Do you have any liverock that you started with, also did you use any live sand?, cycle bacteria?
Do Not put the dead shrimp in!
Believe me you are cycling, either that or your cycle is done but you are just begging to have an ammonia spike if you add that dead shrimp and the yellow tang will feel the ammonia at .5 no buts about it, its leathal, your tang will also feel very confined in that tank.
It is my opinion but you are pushing your bio load to the brink in a 26 gal tank, as they say bad things happen fast. Your ammonia needs to come down either by water changes, or letting your bacteria base catch up with your current bio load.
Fish should be added one at a time, wait two weeks for the bacteria to catch up with the one and add a second...and so forth. The damsal and the clown would be ok to cycle with, however if it had been me I would have just used the dead shrimp to cycle the tank and then add the damsal + clown after the cycle and a water change. I personally would not have added a tang to a 26 gal tank.
Did you test the water for yourself?, did you also have your LFS test it before adding fish? How long have the fish been in there?
Bottom line is I think you moved to quickly here.
Just another opinion
Thomas