It's such a shame that lfs
don't tell you to cycle your tank! Mine didn't even tell me about bacteria!
You can still get your tank cycled with fish in it though. It's just going to take a LOT of water changes!
I did exactly what you did, and I'm just coming through the other side of the cycle.
Your should hopefully be easier than mine too. I've got 7 fish in a 48litre tank. That's a lot of ammonia!
I was doing 50% water changes, 3 times a day.
My cycle is very nearly finished now, and no fishy deaths