I am new coming back to the hobby however I always had an aquarium
when I was younger. Although back then I knew nothing about the
nitrogen cycle. So I got a 28 Gallon tank for xmas and got it all setup and
running. I did a lot of reading to try and just prepare myself since it is
a lot
more complex than I remember. I ended up purchasing two Zebra Danios
to start the tank cycling since I have ready they are fairly hardy fish.
Now
that my tank has cycled I have added 2 more Zebra's. However when I
first got the second pair of Zebra's home I noticed one was a little more
pale than the other one. I didn't think much of it at the time however that
fish had died by the next morning. I didn't notice anything special about
it
however I don't really know anything more than the most common diseases
which I didn't notice. I have since replaced it with an additional fish
however
I have noticed that there seems to be a long(1-2inch) white string hanging
out
of the back of the fish. Then it seems to have disappeared by the time I
get home from work. This has happened on different fish for the last couple
days and I am a little concerned that they might have caught something.
Any advice would be appreciated.

Thanks!

Peter