Cycled means having a beneficial bacterial colony to convert toxic fish waste (ammonia) into nitrIte (still toxic), then another bacterial colonly turns nitrIte into nitrAte.(not nearly as toxic) When you throw away and replace your filter media, you also throw away the beneficial bacteria. Here is a link that will explain cycling more in-depth: http://www.aquariumadvice.com/articl...now/Page2.html
Well, it seems like the problem has been identified. A lot of the people on here have had successful in fish cycles, it just takes a lot more work. If you have anymore questions about the cycle, we are all here to help.
Fish are friends, not food!