Ok I'm getting frustrated with my tank. I have lost fish twice now. After the first time we cleaned the tank and let it run for 1week. Now, again all my fish are dying off one by one. What do I do?
You have to do something called a cycle. This builds up bacteria in the filter that is essential for healthy fish. Leaving the tank running for a week won't cycle it as it needs food (ammonia) and leaving it isn't giving it food. If i were you, i'd give the fish back to the fish shop and press on the link in my signature for info on how to do a fishless cycle
yes! cycling is the way forward, if you have lost fish and not cycled this is why they are dying.
but first:
1) what fish are they?
2) what size tank?
3) what are your water readings?