New to Goldfish...having troubles.

Okay, well ebfore i came to uni i had goldfish in the pond in our back
garden. Both of them lived fine and never had a problem and i used to go and
watch them while studying for my exams.

Well I have final exams coming up, and i live in a flat, so no pond, so i
thought id get a tnak and some goldfish. So off i go to the store. I quizzed
the guy on what to do, my mum had issues keeping ehr fish alive in another
pond so i figured they could be pretty fragile. So i came away with a
smallish tank, gravel for the bottom, a water pump thing and 2 small
goldfish (about an inch and a half to 2 inches long each). The guy told me
to wash the gravel, so i did that. I put it in the bottom of the tank and
spread it out pretty evenly. He told me to half fill the tank or so, add the
pump, then to rest the bag with the fish in the water (we did this back home
with pondfish to let the temperature adjust). Coming home we noticed the bag
had a small leak, but the fish seemed completely undisturbed by this. I elft
the back there for alkmost an hour, then, as the guy in the store had told
me, i took the corner off the bag and left it. After about half an hour both
fish had swum out and were happily swimming around.

Now the guy told me that theyd probably settle near the bottom of the tank
at first, and that i should top it up slowly then leave it (wtihout feeding
the fish) until they were swimming aroudn happily.

Well they swam around msot of the afternoon in the lwoer half of the tank.
The smaller fish settled in one corner, pretty much resting on the gravel,
but staying upright. The other seemed to playa roudn in the bubble stream
form the filter a bit then did the same. I figured this was what the guy had
said, so i didnt worry and when it got dark outside i turned the lights off
and went to bed.

When i woke up this morning the bigger of the fish is dead and the smaller
one is still sat in the same corner at the bottom. he doesnt appear to be
distresse,d gasping for air or anything. he's swum out into the middle a
little then backed away into the corner again a few times, but doesant seem
too happy.

Im wondering what killed the bigger fish, and if it's related to the reason
the smaller one is just sitting in the corner. my girlfriend picked out the
fish that died, so it'd be really useful if i could work out what went
wrong, i dont want to just egt mroe fish if they're going to die. Our water
isnt the greatest, but the shop is in the same area, the guy said it would
be okay, and it seems really clear.

anyone have any suggestions. When the store opens im gonna call them and ask
them about it, and i can go through this afternoon if needs be. I want to
get a couple of nice happy healthy fish, but obviously im not gonna get mroe
fish if they're going to die straight away.

hope soemone can help

Adam