Sick Tetra

Hi all,

I've had these rummynose tetras for over 2 weeks now. They seem very happy and they tend to eat well. One tetra however seems to be very very thin, and the other tetras usually don't swim with it.

The past few days when feeding, I noticed that this lonely tetra didn't eat anything at all.

What should I do with it?

Here's another pic. THe 'sick' tetra is the one at the botttom. You can see that the other tetras look healthy and and as skinny.

quarantine it.... or.... let nature take it's course.

Did you notice what it looked like when it went to the toilet if it was long white and stringy it could be internal parasites, he hasn't lost weight through not eating has he.