Clownfish spit out and not eating

I purchased Spotcintus Clownfish pair on wednesday 3/22/17. I have tried to feed the pair a pellets. I know the pellets is small enough for them to eat because I have small three stripped damselfish and eat the same size of pellets. Then I tried to feed my old mysis shrimp (been outside the package cube maybe have been defrost and froze again) and they still spit out the mysis shrimp. What should I do? I have tried to feed them for 4 days and they just spit out the food. My tank is 25g and it has been running for 14 months. It is the only fish in the tank right now. I have 55 gallon tank still in progress and hasn't been running yet. I will move the clownfish pair once the tank is running. The only tankmate is the skunk cleaner shrimp. lol

Thanks ahead