Hi Cindy S -

I'm not a goldfish expert but some of the
same principles apply to all hobby fish.
You mentioned turning the filter off. That's
not a good idea. The only thing you need to
do with a filter when using medications is
remove the carbon cartridge, which usually
isn't needed anyway.

You mentioned the tank being up only a
few weeks or a month. Partial water changes
need to be done weekly, especially with
"dirty" fish like goldfish.

There are a number of small (not expensive)
books on goldfish care, available at pet
stores and bookstores. If you don't already
have one, I'd suggest getting one or two. I'm
a big fan of reference books for hobbies.

I have cats and although litter boxes aren't in
the same room, there are five boxes scattered
about the house. I wouldn't worry if I were
you about the ammonia from litter boxes
ending up in your goldfish tank.

As a wild guess, I would suggest that putting
two goldfish together into water that probably
was not cycled first stressed out your fish. It
happened your original fish was more sensitive
since it had been alone in its own water for so
long (possible old tank syndrome, as others
mentioned), whereas the new fish had come from
a tank with a bunch of other fish.

When you test the water you want nitrAtes but
not nitrItes or ammonia. Nitrates should range
around 20, I think, for goldfish. (I try to keep it
at that level or lower for tropical fish.)

I hope your fish will be ok. Let us know
what happens.

Gail
in Texas