Green faced cardinal

[florist2001]

I have done a lot of searching this morning and found nothing on this topic... anyone else ever experience this???

Yesterday, I introduced 3 pajama cardinals to my 55g tank. The seem happy, and are eating fine, but this morning, one of them had a dark green face.. like something out of a cartoon when someones about to... you get the idea...

Any ideas??

Thanks in advance, Amanda